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<a href="concurrent__task__loop_8hpp.html">Go to the documentation of this file.</a><div class="fragment"><div class="line"><a id="l00001" name="l00001"></a><span class="lineno">    1</span><span class="comment">/* Flow</span></div>
<div class="line"><a id="l00002" name="l00002"></a><span class="lineno">    2</span><span class="comment"> * Copyright 2023 Akamai Technologies, Inc.</span></div>
<div class="line"><a id="l00003" name="l00003"></a><span class="lineno">    3</span><span class="comment"> *</span></div>
<div class="line"><a id="l00004" name="l00004"></a><span class="lineno">    4</span><span class="comment"> * Licensed under the Apache License, Version 2.0 (the</span></div>
<div class="line"><a id="l00005" name="l00005"></a><span class="lineno">    5</span><span class="comment"> * &quot;License&quot;); you may not use this file except in</span></div>
<div class="line"><a id="l00006" name="l00006"></a><span class="lineno">    6</span><span class="comment"> * compliance with the License.  You may obtain a copy</span></div>
<div class="line"><a id="l00007" name="l00007"></a><span class="lineno">    7</span><span class="comment"> * of the License at</span></div>
<div class="line"><a id="l00008" name="l00008"></a><span class="lineno">    8</span><span class="comment"> *</span></div>
<div class="line"><a id="l00009" name="l00009"></a><span class="lineno">    9</span><span class="comment"> *   https://www.apache.org/licenses/LICENSE-2.0</span></div>
<div class="line"><a id="l00010" name="l00010"></a><span class="lineno">   10</span><span class="comment"> *</span></div>
<div class="line"><a id="l00011" name="l00011"></a><span class="lineno">   11</span><span class="comment"> * Unless required by applicable law or agreed to in</span></div>
<div class="line"><a id="l00012" name="l00012"></a><span class="lineno">   12</span><span class="comment"> * writing, software distributed under the License is</span></div>
<div class="line"><a id="l00013" name="l00013"></a><span class="lineno">   13</span><span class="comment"> * distributed on an &quot;AS IS&quot; BASIS, WITHOUT WARRANTIES OR</span></div>
<div class="line"><a id="l00014" name="l00014"></a><span class="lineno">   14</span><span class="comment"> * CONDITIONS OF ANY KIND, either express or implied.</span></div>
<div class="line"><a id="l00015" name="l00015"></a><span class="lineno">   15</span><span class="comment"> * See the License for the specific language governing</span></div>
<div class="line"><a id="l00016" name="l00016"></a><span class="lineno">   16</span><span class="comment"> * permissions and limitations under the License. */</span></div>
<div class="line"><a id="l00017" name="l00017"></a><span class="lineno">   17</span><span class="comment"></span> </div>
<div class="line"><a id="l00018" name="l00018"></a><span class="lineno">   18</span><span class="comment">/// @file</span></div>
<div class="line"><a id="l00019" name="l00019"></a><span class="lineno">   19</span><span class="comment"></span><span class="preprocessor">#pragma once</span></div>
<div class="line"><a id="l00020" name="l00020"></a><span class="lineno">   20</span> </div>
<div class="line"><a id="l00021" name="l00021"></a><span class="lineno">   21</span><span class="preprocessor">#include &quot;<a class="code" href="async__fwd_8hpp.html">flow/async/async_fwd.hpp</a>&quot;</span></div>
<div class="line"><a id="l00022" name="l00022"></a><span class="lineno">   22</span><span class="preprocessor">#include &quot;<a class="code" href="op_8hpp.html">flow/async/op.hpp</a>&quot;</span></div>
<div class="line"><a id="l00023" name="l00023"></a><span class="lineno">   23</span><span class="preprocessor">#include &quot;<a class="code" href="sched__task__fwd_8hpp.html">flow/util/sched_task_fwd.hpp</a>&quot;</span></div>
<div class="line"><a id="l00024" name="l00024"></a><span class="lineno">   24</span><span class="preprocessor">#include &quot;<a class="code" href="util_2util_8hpp.html">flow/util/util.hpp</a>&quot;</span></div>
<div class="line"><a id="l00025" name="l00025"></a><span class="lineno">   25</span> </div>
<div class="line"><a id="l00026" name="l00026"></a><span class="lineno">   26</span><span class="keyword">namespace </span><a class="code hl_namespace" href="namespaceflow_1_1async.html">flow::async</a></div>
<div class="line"><a id="l00027" name="l00027"></a><span class="lineno">   27</span>{</div>
<div class="line"><a id="l00028" name="l00028"></a><span class="lineno">   28</span> </div>
<div class="line"><a id="l00029" name="l00029"></a><span class="lineno">   29</span><span class="comment">// Types.</span></div>
<div class="line"><a id="l00030" name="l00030"></a><span class="lineno">   30</span><span class="comment"></span> </div>
<div class="line"><a id="l00031" name="l00031"></a><span class="lineno">   31</span><span class="comment">/**</span></div>
<div class="line"><a id="l00032" name="l00032"></a><span class="lineno">   32</span><span class="comment"> * The core flow::async interface, providing an optionally multi-threaded thread pool onto which runnable `Task`s,</span></div>
<div class="line"><a id="l00033" name="l00033"></a><span class="lineno">   33</span><span class="comment"> * optionally arranged into concurrency-avoiding `Op`s, can be boost.asio-posted for subsequent execution.</span></div>
<div class="line"><a id="l00034" name="l00034"></a><span class="lineno">   34</span><span class="comment"> *</span></div>
<div class="line"><a id="l00035" name="l00035"></a><span class="lineno">   35</span><span class="comment"> * ### Thread safety ###</span></div>
<div class="line"><a id="l00036" name="l00036"></a><span class="lineno">   36</span><span class="comment"> * All methods are thread-safe for read-write on a shared Concurrent_task_loop, after its ctor returns, unless</span></div>
<div class="line"><a id="l00037" name="l00037"></a><span class="lineno">   37</span><span class="comment"> * otherwise specified (but read on).  This is highly significant, just as it is highly significant that boost.asio&#39;s</span></div>
<div class="line"><a id="l00038" name="l00038"></a><span class="lineno">   38</span><span class="comment"> * `post(Task_engine&amp;)` is similarly thread-safe.  However, it is *not* safe to call either stop() or start()</span></div>
<div class="line"><a id="l00039" name="l00039"></a><span class="lineno">   39</span><span class="comment"> * concurrently with itself or the other of the two, on the same Concurrent_task_loop.</span></div>
<div class="line"><a id="l00040" name="l00040"></a><span class="lineno">   40</span><span class="comment"> *</span></div>
<div class="line"><a id="l00041" name="l00041"></a><span class="lineno">   41</span><span class="comment"> * ### First, select subclass to instantiate ###</span></div>
<div class="line"><a id="l00042" name="l00042"></a><span class="lineno">   42</span><span class="comment"> * Whenever the user needs a pool of task-executing threads, meaning threads awaiting user-supplied work, to be</span></div>
<div class="line"><a id="l00043" name="l00043"></a><span class="lineno">   43</span><span class="comment"> * `post()`ed (etc.) in the boost.asio sense, they&#39;ll create a concrete subclass of this interface</span></div>
<div class="line"><a id="l00044" name="l00044"></a><span class="lineno">   44</span><span class="comment"> * (the choice perhaps based on configuration, e.g.).  The choice of subclass determines how tasks will be scheduled</span></div>
<div class="line"><a id="l00045" name="l00045"></a><span class="lineno">   45</span><span class="comment"> * internally across threads, but the user need not worry about that after construction.</span></div>
<div class="line"><a id="l00046" name="l00046"></a><span class="lineno">   46</span><span class="comment"> *</span></div>
<div class="line"><a id="l00047" name="l00047"></a><span class="lineno">   47</span><span class="comment"> * If your task loop is fundamentally single-threaded -- which is *extremely* common and *typically* does *not*</span></div>
<div class="line"><a id="l00048" name="l00048"></a><span class="lineno">   48</span><span class="comment"> * generalize to a multi-threaded one easily -- then instead use the adapter Single_thread_task_loop which is *not*</span></div>
<div class="line"><a id="l00049" name="l00049"></a><span class="lineno">   49</span><span class="comment"> * a part of Concurrent_task_loop hierarchy but *does* use the relevant parts of it internally.</span></div>
<div class="line"><a id="l00050" name="l00050"></a><span class="lineno">   50</span><span class="comment"> *</span></div>
<div class="line"><a id="l00051" name="l00051"></a><span class="lineno">   51</span><span class="comment"> * If you choose Single_thread_task_loop then it is not necessary to read further.</span></div>
<div class="line"><a id="l00052" name="l00052"></a><span class="lineno">   52</span><span class="comment"> *</span></div>
<div class="line"><a id="l00053" name="l00053"></a><span class="lineno">   53</span><span class="comment"> * ### Next, call start() ###</span></div>
<div class="line"><a id="l00054" name="l00054"></a><span class="lineno">   54</span><span class="comment"> * This starts the actual threads in the thread pool.  Hence subsequent `post(F)` (etc.) will cause `F()` to</span></div>
<div class="line"><a id="l00055" name="l00055"></a><span class="lineno">   55</span><span class="comment"> * be able to run in one of the threads.  Some advanced points:</span></div>
<div class="line"><a id="l00056" name="l00056"></a><span class="lineno">   56</span><span class="comment"> *   - You may post() (etc.) before start().  This will do no work but queue it up until start().</span></div>
<div class="line"><a id="l00057" name="l00057"></a><span class="lineno">   57</span><span class="comment"> *   - You may call stop() to synchronously, gracefully exit the threads.  Any `post()`ed (etc.) that hadn&#39;t</span></div>
<div class="line"><a id="l00058" name="l00058"></a><span class="lineno">   58</span><span class="comment"> *     yet run will remain queued.  Any post() (etc.) until the next start() will (again) do no work and (again)</span></div>
<div class="line"><a id="l00059" name="l00059"></a><span class="lineno">   59</span><span class="comment"> *     remain queued until start().</span></div>
<div class="line"><a id="l00060" name="l00060"></a><span class="lineno">   60</span><span class="comment"> *   - If you save the (ref-counted) util::Task_engine from task_engine() or from an async::Op via</span></div>
<div class="line"><a id="l00061" name="l00061"></a><span class="lineno">   61</span><span class="comment"> *     op_to_exec_ctx(), you may use it even after `*this` is destroyed.  It is then your responsibility to</span></div>
<div class="line"><a id="l00062" name="l00062"></a><span class="lineno">   62</span><span class="comment"> *     start thread(s) in which to actually execute its tasks.  Any queued tasks on the `Task_engine` will remain</span></div>
<div class="line"><a id="l00063" name="l00063"></a><span class="lineno">   63</span><span class="comment"> *     queued until then.</span></div>
<div class="line"><a id="l00064" name="l00064"></a><span class="lineno">   64</span><span class="comment"> *   - (This start/stop/run/post paradigm may be familiar to boost.asio (particularly `boost::asio::io_context`) users.)</span></div>
<div class="line"><a id="l00065" name="l00065"></a><span class="lineno">   65</span><span class="comment"> *</span></div>
<div class="line"><a id="l00066" name="l00066"></a><span class="lineno">   66</span><span class="comment"> * ### Next, post() tasks on it: create_op() to group task into operations ###</span></div>
<div class="line"><a id="l00067" name="l00067"></a><span class="lineno">   67</span><span class="comment"> * One can post() a task (in the same way one would simply `post(Task_engine&amp;)`).  If one wants to execute an async</span></div>
<div class="line"><a id="l00068" name="l00068"></a><span class="lineno">   68</span><span class="comment"> * op with 2+ non-concurrent tasks, they would pass the same async::Op to post() for each of the aforementioned 2+</span></div>
<div class="line"><a id="l00069" name="l00069"></a><span class="lineno">   69</span><span class="comment"> * `Task`s (which are simply `void` no-arg functions basically).  An async::Op can be created</span></div>
<div class="line"><a id="l00070" name="l00070"></a><span class="lineno">   70</span><span class="comment"> * via create_op(); or if the task must be pinned to a specific pre-made per-software-thread async::Op,</span></div>
<div class="line"><a id="l00071" name="l00071"></a><span class="lineno">   71</span><span class="comment"> * these are accessible via per_thread_ops().</span></div>
<div class="line"><a id="l00072" name="l00072"></a><span class="lineno">   72</span><span class="comment"> *</span></div>
<div class="line"><a id="l00073" name="l00073"></a><span class="lineno">   73</span><span class="comment"> * New applications should strive to use only create_op() and not touch the advanced-yet-legacy-ish</span></div>
<div class="line"><a id="l00074" name="l00074"></a><span class="lineno">   74</span><span class="comment"> * per_thread_ops() facility.  In a classic async-task-based-event-loop algorithm, it should be sufficient to</span></div>
<div class="line"><a id="l00075" name="l00075"></a><span class="lineno">   75</span><span class="comment"> * execute `Task`s -- sprinkling in `Op` tags when certain tasks together comprise multi-async-step ops --</span></div>
<div class="line"><a id="l00076" name="l00076"></a><span class="lineno">   76</span><span class="comment"> * via one of the post() overloads.  Hence simply make an `Op` via create_op() to associate `Task`s with each other,</span></div>
<div class="line"><a id="l00077" name="l00077"></a><span class="lineno">   77</span><span class="comment"> * and that should be enough for most async algorithms.</span></div>
<div class="line"><a id="l00078" name="l00078"></a><span class="lineno">   78</span><span class="comment"> *</span></div>
<div class="line"><a id="l00079" name="l00079"></a><span class="lineno">   79</span><span class="comment"> * Note also the optional `Synchronicity synchronicity` argument to the `post()` methods.  By default this acts</span></div>
<div class="line"><a id="l00080" name="l00080"></a><span class="lineno">   80</span><span class="comment"> * like regular `post(Task_engine&amp;)`, but you can also access `dispatch(Task_engine&amp;)` type of behavior;</span></div>
<div class="line"><a id="l00081" name="l00081"></a><span class="lineno">   81</span><span class="comment"> * you can wait for the task to complete using yet another mode.  The latter feature,</span></div>
<div class="line"><a id="l00082" name="l00082"></a><span class="lineno">   82</span><span class="comment"> * Synchronicity::S_ASYNC_AND_AWAIT_CONCURRENT_COMPLETION, may be particularly helpful at initialization time, such</span></div>
<div class="line"><a id="l00083" name="l00083"></a><span class="lineno">   83</span><span class="comment"> * as if one needs to perform some startup tasks in the new thread(s) before continuing to general work on</span></div>
<div class="line"><a id="l00084" name="l00084"></a><span class="lineno">   84</span><span class="comment"> * the loop.  E.g., subclasses might, for convenience, wrap this ability in their constructors, so that the user can</span></div>
<div class="line"><a id="l00085" name="l00085"></a><span class="lineno">   85</span><span class="comment"> * optionally provide an initializing task to run before the ctor returns.</span></div>
<div class="line"><a id="l00086" name="l00086"></a><span class="lineno">   86</span><span class="comment"> *</span></div>
<div class="line"><a id="l00087" name="l00087"></a><span class="lineno">   87</span><span class="comment"> * Lastly Synchronicity::S_ASYNC_AND_AWAIT_CONCURRENT_START may be quite helpful in ensuring a certain</span></div>
<div class="line"><a id="l00088" name="l00088"></a><span class="lineno">   88</span><span class="comment"> * task definitely does run -- without waiting for it to actually run, but merely *begin* to run.  More specifically</span></div>
<div class="line"><a id="l00089" name="l00089"></a><span class="lineno">   89</span><span class="comment"> * `L.post(F, Synchronicity::S_ASYNC_AND_AWAIT_CONCURRENT_START); L.stop();` will ensure `F()` will run at some point --</span></div>
<div class="line"><a id="l00090" name="l00090"></a><span class="lineno">   90</span><span class="comment"> * but not wait for its completion.  `L.post(F); L.stop();` will not ensure this at all; whether it does or not</span></div>
<div class="line"><a id="l00091" name="l00091"></a><span class="lineno">   91</span><span class="comment"> * is a matter of luck.  `L.post(F, Synchronicity::S_ASYNC_AND_AWAIT_CONCURRENT_COMPLETION); L.stop();` *will* ensure</span></div>
<div class="line"><a id="l00092" name="l00092"></a><span class="lineno">   92</span><span class="comment"> * it but also force a wait until `F()` finishes which may not be necessary and hence increases latency/responsiveness</span></div>
<div class="line"><a id="l00093" name="l00093"></a><span class="lineno">   93</span><span class="comment"> * in the calling thread.</span></div>
<div class="line"><a id="l00094" name="l00094"></a><span class="lineno">   94</span><span class="comment"> *</span></div>
<div class="line"><a id="l00095" name="l00095"></a><span class="lineno">   95</span><span class="comment"> * ### And/or: Use per_thread_ops() to associate `Task`s with specific threads ###</span></div>
<div class="line"><a id="l00096" name="l00096"></a><span class="lineno">   96</span><span class="comment"> * There are cases when the simple, conceptual approach just described (using create_op() only, if an `Op` is even</span></div>
<div class="line"><a id="l00097" name="l00097"></a><span class="lineno">   97</span><span class="comment"> * desired at all) is not sufficient.  Another approach is to pre-create N `Op`s, where N is the number of threads</span></div>
<div class="line"><a id="l00098" name="l00098"></a><span class="lineno">   98</span><span class="comment"> * in the thread pool, and instead of create_op() one can randomly choose one of those N `Op`s and `post()` onto that</span></div>
<div class="line"><a id="l00099" name="l00099"></a><span class="lineno">   99</span><span class="comment"> * one (an `Op` is an `Op` regardless of how it was obtained).  Informally, there are 2 known categories of use cases</span></div>
<div class="line"><a id="l00100" name="l00100"></a><span class="lineno">  100</span><span class="comment"> * for this, with overlap:</span></div>
<div class="line"><a id="l00101" name="l00101"></a><span class="lineno">  101</span><span class="comment"> *   - The legacy use case: Major daemons exist that were architected decades before flow::async was even conceived,</span></div>
<div class="line"><a id="l00102" name="l00102"></a><span class="lineno">  102</span><span class="comment"> *     so they understandably achieve some of the same aims (to wit, non-concurrency of tasks in an op) by working with</span></div>
<div class="line"><a id="l00103" name="l00103"></a><span class="lineno">  103</span><span class="comment"> *     the lower-level/less abstract notion of a thread in a pool.  Basically, if an `Op` corresponds to a worker</span></div>
<div class="line"><a id="l00104" name="l00104"></a><span class="lineno">  104</span><span class="comment"> *     thread specifically, then internally 2 `Task`s being assigned to that 1 `Op` would just mean executing them</span></div>
<div class="line"><a id="l00105" name="l00105"></a><span class="lineno">  105</span><span class="comment"> *     on that `Op`&#39;s corresponding worker thread; threads are serial by definition, so the `Op` semantics are trivially</span></div>
<div class="line"><a id="l00106" name="l00106"></a><span class="lineno">  106</span><span class="comment"> *     satisfied.  So to support such legacy designs, the per-thread-pre-created in per_thread_ops() allow user to</span></div>
<div class="line"><a id="l00107" name="l00107"></a><span class="lineno">  107</span><span class="comment"> *     obtain either a randomly chosen or a specifically indexed 1 of N per-thread async::Op.</span></div>
<div class="line"><a id="l00108" name="l00108"></a><span class="lineno">  108</span><span class="comment"> *     - Example: Suppose a multi-threaded memory-caching server has a central data store and explicitly</span></div>
<div class="line"><a id="l00109" name="l00109"></a><span class="lineno">  109</span><span class="comment"> *       thread-local copies (periodically synchronized with the central one) thereof.  With such a setup, it&#39;s</span></div>
<div class="line"><a id="l00110" name="l00110"></a><span class="lineno">  110</span><span class="comment"> *       a no-brainer to throw all work on a request that was originally assigned to thread 3 (random) of N *also* to</span></div>
<div class="line"><a id="l00111" name="l00111"></a><span class="lineno">  111</span><span class="comment"> *       per-thread Op #3 of N, for all `Task`s comprising that request&#39;s handling:  Since all tasks operating in</span></div>
<div class="line"><a id="l00112" name="l00112"></a><span class="lineno">  112</span><span class="comment"> *       `Op` (therefore thread) #3 by definition execute non-concurrently, no locks are necessary when working</span></div>
<div class="line"><a id="l00113" name="l00113"></a><span class="lineno">  113</span><span class="comment"> *       with thread #3&#39;s thread-local object store copy.  Simply, only thread `i` of N will ever touch object store</span></div>
<div class="line"><a id="l00114" name="l00114"></a><span class="lineno">  114</span><span class="comment"> *       `i` of N, to the extent it can be explicitly declared thread-local (`thread_local` in C++11, or similar).</span></div>
<div class="line"><a id="l00115" name="l00115"></a><span class="lineno">  115</span><span class="comment"> *   - The thread-to-thread communication use case: This has come up in practice: If daemon 1 has N producer threads,</span></div>
<div class="line"><a id="l00116" name="l00116"></a><span class="lineno">  116</span><span class="comment"> *     and daemon 2 has N consumer threads, then one can set up N IPC queues, where thread `i` in either process</span></div>
<div class="line"><a id="l00117" name="l00117"></a><span class="lineno">  117</span><span class="comment"> *     accessing (writing and reading, respectively) only queue `i`.  Then -- assuming the queue itself is</span></div>
<div class="line"><a id="l00118" name="l00118"></a><span class="lineno">  118</span><span class="comment"> *     safe against 1 read occurring concurrently with 1 write -- no further locking is required.  Basically,</span></div>
<div class="line"><a id="l00119" name="l00119"></a><span class="lineno">  119</span><span class="comment"> *     thread `i` in daemon 1 deals with thread `i` in daemon 2, using a dedicated lock-free thread-`i`-access-only</span></div>
<div class="line"><a id="l00120" name="l00120"></a><span class="lineno">  120</span><span class="comment"> *     IPC queue.</span></div>
<div class="line"><a id="l00121" name="l00121"></a><span class="lineno">  121</span><span class="comment"> *</span></div>
<div class="line"><a id="l00122" name="l00122"></a><span class="lineno">  122</span><span class="comment"> * ### Timers have similarly streamlined API: schedule_task_from_now() ###</span></div>
<div class="line"><a id="l00123" name="l00123"></a><span class="lineno">  123</span><span class="comment"> * post() is absolutely core, of course.  However obviously sometimes one needs to wait *asynchronously* for some kind</span></div>
<div class="line"><a id="l00124" name="l00124"></a><span class="lineno">  124</span><span class="comment"> * of event and THEN execute a task on that event.  In particular, executing it simply after some specific time period</span></div>
<div class="line"><a id="l00125" name="l00125"></a><span class="lineno">  125</span><span class="comment"> * passes is common and has a dedicated API.  This is called *scheduling a task* in our parlance.</span></div>
<div class="line"><a id="l00126" name="l00126"></a><span class="lineno">  126</span><span class="comment"> *</span></div>
<div class="line"><a id="l00127" name="l00127"></a><span class="lineno">  127</span><span class="comment"> * If you want to schedule a task, first decide whether you need certain advanced capabilities.  This is explained in</span></div>
<div class="line"><a id="l00128" name="l00128"></a><span class="lineno">  128</span><span class="comment"> * the doc header for util::schedule_task_from_now().  If you decide you need advanced capabilities, then skip to the</span></div>
<div class="line"><a id="l00129" name="l00129"></a><span class="lineno">  129</span><span class="comment"> * next subsection below, about general boost.asio I/O objects.  Most of the time you won&#39;t, in which case read on:</span></div>
<div class="line"><a id="l00130" name="l00130"></a><span class="lineno">  130</span><span class="comment"> *</span></div>
<div class="line"><a id="l00131" name="l00131"></a><span class="lineno">  131</span><span class="comment"> * schedule_from_now() and schedule_at() in this Concurrent_task_loop interface provide all the capabilities of</span></div>
<div class="line"><a id="l00132" name="l00132"></a><span class="lineno">  132</span><span class="comment"> * `util::schedule[d]_task*()` API.  (Reminder: This includes canceling and short-firing the task with ease, more</span></div>
<div class="line"><a id="l00133" name="l00133"></a><span class="lineno">  133</span><span class="comment"> * ease than if using the full on I/O util::Timer, which is -- again -- explained below.)  Just as with post(), there</span></div>
<div class="line"><a id="l00134" name="l00134"></a><span class="lineno">  134</span><span class="comment"> * is 1 version of each method for single tasks; and and 1 for operating within an async::Op, meaning the timer</span></div>
<div class="line"><a id="l00135" name="l00135"></a><span class="lineno">  135</span><span class="comment"> * completion handler.</span></div>
<div class="line"><a id="l00136" name="l00136"></a><span class="lineno">  136</span><span class="comment"> *</span></div>
<div class="line"><a id="l00137" name="l00137"></a><span class="lineno">  137</span><span class="comment"> * ### General boost.asio objects can be fully used with Concurrent_task_loop ###</span></div>
<div class="line"><a id="l00138" name="l00138"></a><span class="lineno">  138</span><span class="comment"> * Finally, there&#39;s general boost.asio &quot;I/O object&quot; work.  An I/O object is usually a class -- within boost.asio itself</span></div>
<div class="line"><a id="l00139" name="l00139"></a><span class="lineno">  139</span><span class="comment"> * or a custom object -- with 1 or more *asynchronous action* methods, always named in the style `async_*()`.  To show</span></div>
<div class="line"><a id="l00140" name="l00140"></a><span class="lineno">  140</span><span class="comment"> * how one would do this with Concurrent_task_loop, let&#39;s do it in somewhat formal fashion:</span></div>
<div class="line"><a id="l00141" name="l00141"></a><span class="lineno">  141</span><span class="comment"> *</span></div>
<div class="line"><a id="l00142" name="l00142"></a><span class="lineno">  142</span><span class="comment"> * Suppose you have boost.asio object X, for example `boost::asio::ip::tcp::socket` (in boost.asio itself) and</span></div>
<div class="line"><a id="l00143" name="l00143"></a><span class="lineno">  143</span><span class="comment"> * flow::net_flow::asio::Peer_socket (a custom one), and we want to perform an `async_A()` action, which waits</span></div>
<div class="line"><a id="l00144" name="l00144"></a><span class="lineno">  144</span><span class="comment"> * asynchronously for some event (e.g., a successful `tcp::socket::async_receive()` or</span></div>
<div class="line"><a id="l00145" name="l00145"></a><span class="lineno">  145</span><span class="comment"> * `net_flow::asio::Peer_socket::async_send()`, and then executes a *completion handler* task F:</span></div>
<div class="line"><a id="l00146" name="l00146"></a><span class="lineno">  146</span><span class="comment"> *</span></div>
<div class="line"><a id="l00147" name="l00147"></a><span class="lineno">  147</span><span class="comment"> *   ~~~</span></div>
<div class="line"><a id="l00148" name="l00148"></a><span class="lineno">  148</span><span class="comment"> *   flow::util::Task_engine E; // boost.asio user works directly with a Task_engine E running in 1+ threads.</span></div>
<div class="line"><a id="l00149" name="l00149"></a><span class="lineno">  149</span><span class="comment"> *   ...</span></div>
<div class="line"><a id="l00150" name="l00150"></a><span class="lineno">  150</span><span class="comment"> *   X_type X(&amp;E);</span></div>
<div class="line"><a id="l00151" name="l00151"></a><span class="lineno">  151</span><span class="comment"> *   // A_target represents 0 or more mutable data structures (e.g., received-data target buffer) that sync_A() would</span></div>
<div class="line"><a id="l00152" name="l00152"></a><span class="lineno">  152</span><span class="comment"> *   //   modify in the background.</span></div>
<div class="line"><a id="l00153" name="l00153"></a><span class="lineno">  153</span><span class="comment"> *   // A_settings represents 0 or more immutable/by-value args controlling behavior of the background sync_A() action.</span></div>
<div class="line"><a id="l00154" name="l00154"></a><span class="lineno">  154</span><span class="comment"> *   X.async_A(&amp;A_target, A_settings, F);</span></div>
<div class="line"><a id="l00155" name="l00155"></a><span class="lineno">  155</span><span class="comment"> *   // Equivalent of X.sync_A(&amp;A_target, A_settings) is now executing in background via Task_engine E!</span></div>
<div class="line"><a id="l00156" name="l00156"></a><span class="lineno">  156</span><span class="comment"> *   // Once done, it will act as if one called, from an unspecified thread: F(err_code, A_more_result_info).</span></div>
<div class="line"><a id="l00157" name="l00157"></a><span class="lineno">  157</span><span class="comment"> *   //   - Error_code err_code is the success/failure result code.  In particular, `!err_code == true` on success.</span></div>
<div class="line"><a id="l00158" name="l00158"></a><span class="lineno">  158</span><span class="comment"> *   //   - A_more_result_info represents 0 or more other bits of immutable/by-copy info indicating the results of</span></div>
<div class="line"><a id="l00159" name="l00159"></a><span class="lineno">  159</span><span class="comment"> *   //     the background action.  For example, both `tcp::socket::async_receive()` and</span></div>
<div class="line"><a id="l00160" name="l00160"></a><span class="lineno">  160</span><span class="comment"> *   //     `net_flow::Peer_socket::async_send()` will call `F(err_code, n)`, where `size_t n` is the # of bytes</span></div>
<div class="line"><a id="l00161" name="l00161"></a><span class="lineno">  161</span><span class="comment"> *   //     received or sent respectively.</span></div>
<div class="line"><a id="l00162" name="l00162"></a><span class="lineno">  162</span><span class="comment"> *   ~~~</span></div>
<div class="line"><a id="l00163" name="l00163"></a><span class="lineno">  163</span><span class="comment"> *</span></div>
<div class="line"><a id="l00164" name="l00164"></a><span class="lineno">  164</span><span class="comment"> * That&#39;s the setup and should be familiar to boost.asio I/O object users.  (Note that util::Timer is a (relatively</span></div>
<div class="line"><a id="l00165" name="l00165"></a><span class="lineno">  165</span><span class="comment"> * simple) I/O object itself; it lacks `A_settings` (one makes a call like `expires_at()` separately before the</span></div>
<div class="line"><a id="l00166" name="l00166"></a><span class="lineno">  166</span><span class="comment"> * actual async action) and `A_more_result_info` (as `err_code` is sufficient) in particular.  It also lacks</span></div>
<div class="line"><a id="l00167" name="l00167"></a><span class="lineno">  167</span><span class="comment"> * any `A_target`.  It&#39;s clearly the degenerate example of an I/O object action.)  So how to write the</span></div>
<div class="line"><a id="l00168" name="l00168"></a><span class="lineno">  168</span><span class="comment"> * above when working with a Concurrent_task_loop instead of `Task_engine`?</span></div>
<div class="line"><a id="l00169" name="l00169"></a><span class="lineno">  169</span><span class="comment"> *</span></div>
<div class="line"><a id="l00170" name="l00170"></a><span class="lineno">  170</span><span class="comment"> *   ~~~</span></div>
<div class="line"><a id="l00171" name="l00171"></a><span class="lineno">  171</span><span class="comment"> *   flow::async::Concurrent_task_loop L; // Work with generalized thread pool L, not a Task_engine E.</span></div>
<div class="line"><a id="l00172" name="l00172"></a><span class="lineno">  172</span><span class="comment"> *   ...</span></div>
<div class="line"><a id="l00173" name="l00173"></a><span class="lineno">  173</span><span class="comment"> *   // ATTN!  A Task_engine is needed by boost.asio?  Use our API -- task_engine() -- to get one.</span></div>
<div class="line"><a id="l00174" name="l00174"></a><span class="lineno">  174</span><span class="comment"> *   X_type X(L.task_engine());</span></div>
<div class="line"><a id="l00175" name="l00175"></a><span class="lineno">  175</span><span class="comment"> *   X.async_A(&amp;A_target, A_settings, F);</span></div>
<div class="line"><a id="l00176" name="l00176"></a><span class="lineno">  176</span><span class="comment"> *   ~~~</span></div>
<div class="line"><a id="l00177" name="l00177"></a><span class="lineno">  177</span><span class="comment"> *</span></div>
<div class="line"><a id="l00178" name="l00178"></a><span class="lineno">  178</span><span class="comment"> * Almost everything is the same!  Just need to call that API to obtain a `Task_engine` to use.  As a result:</span></div>
<div class="line"><a id="l00179" name="l00179"></a><span class="lineno">  179</span><span class="comment"> *   - The background action, the equivalent of `X.sync_A()`, will be performed by some unspecified code in some</span></div>
<div class="line"><a id="l00180" name="l00180"></a><span class="lineno">  180</span><span class="comment"> *     unknown thread.  We don&#39;t care how with boost.asio directly, and we don&#39;t care how with Concurrent_task_loop</span></div>
<div class="line"><a id="l00181" name="l00181"></a><span class="lineno">  181</span><span class="comment"> *     either.</span></div>
<div class="line"><a id="l00182" name="l00182"></a><span class="lineno">  182</span><span class="comment"> *   - Then, for some `async_A()`s it will modify `A_target`.  This, too, will be done by an unspecified thread</span></div>
<div class="line"><a id="l00183" name="l00183"></a><span class="lineno">  183</span><span class="comment"> *     *with no locking guarantees*.  Hence, one must not access `A_target` from application threads.  As wit</span></div>
<div class="line"><a id="l00184" name="l00184"></a><span class="lineno">  184</span><span class="comment"> *     boost.asio direct use, this is typical.  For example no app code would access the target data buffer of a</span></div>
<div class="line"><a id="l00185" name="l00185"></a><span class="lineno">  185</span><span class="comment"> *     receive operation.</span></div>
<div class="line"><a id="l00186" name="l00186"></a><span class="lineno">  186</span><span class="comment"> *   - Finally, `F()` will be posted on completion via `Task_engine L.task_engine()`.  Of course we guarantee it</span></div>
<div class="line"><a id="l00187" name="l00187"></a><span class="lineno">  187</span><span class="comment"> *     will be in some thread in the thread pool `L`.</span></div>
<div class="line"><a id="l00188" name="l00188"></a><span class="lineno">  188</span><span class="comment"> *</span></div>
<div class="line"><a id="l00189" name="l00189"></a><span class="lineno">  189</span><span class="comment"> * Finally, then, suppose the original snippet above is modified to use a `Strand`, to guarantee non-concurrency with</span></div>
<div class="line"><a id="l00190" name="l00190"></a><span class="lineno">  190</span><span class="comment"> * some other boost.asio handler(s).  This would look like:</span></div>
<div class="line"><a id="l00191" name="l00191"></a><span class="lineno">  191</span><span class="comment"> *</span></div>
<div class="line"><a id="l00192" name="l00192"></a><span class="lineno">  192</span><span class="comment"> *   ~~~</span></div>
<div class="line"><a id="l00193" name="l00193"></a><span class="lineno">  193</span><span class="comment"> *   flow::util::Task_engine E;</span></div>
<div class="line"><a id="l00194" name="l00194"></a><span class="lineno">  194</span><span class="comment"> *   flow::util::Strand S(&amp;E); // Create a Strand that guarantees non-concurrency of handlers posted onto Task_engine E.</span></div>
<div class="line"><a id="l00195" name="l00195"></a><span class="lineno">  195</span><span class="comment"> *   ...</span></div>
<div class="line"><a id="l00196" name="l00196"></a><span class="lineno">  196</span><span class="comment"> *   X_type X(&amp;E);</span></div>
<div class="line"><a id="l00197" name="l00197"></a><span class="lineno">  197</span><span class="comment"> *   X.async_A(&amp;A_target, A_settings, boost::asio::bind_executor(S, F));</span></div>
<div class="line"><a id="l00198" name="l00198"></a><span class="lineno">  198</span><span class="comment"> *   ...</span></div>
<div class="line"><a id="l00199" name="l00199"></a><span class="lineno">  199</span><span class="comment"> *   Y_type Y(&amp;E);</span></div>
<div class="line"><a id="l00200" name="l00200"></a><span class="lineno">  200</span><span class="comment"> *   Y.async_B(&amp;B_target, B_settings, boost::asio::bind_executor(S, G));</span></div>
<div class="line"><a id="l00201" name="l00201"></a><span class="lineno">  201</span><span class="comment"> *   // X.sync_A() and Y.sync_B() are executing in background; F() and G() will run on respective completion;</span></div>
<div class="line"><a id="l00202" name="l00202"></a><span class="lineno">  202</span><span class="comment"> *   // but F() and G() shall run non-concurrently by virtue of being wrapped by the same Strand: S.</span></div>
<div class="line"><a id="l00203" name="l00203"></a><span class="lineno">  203</span><span class="comment"> *   ~~~</span></div>
<div class="line"><a id="l00204" name="l00204"></a><span class="lineno">  204</span><span class="comment"> *</span></div>
<div class="line"><a id="l00205" name="l00205"></a><span class="lineno">  205</span><span class="comment"> * To accomplish this with a `Concurrent_task_loop L`:</span></div>
<div class="line"><a id="l00206" name="l00206"></a><span class="lineno">  206</span><span class="comment"> *</span></div>
<div class="line"><a id="l00207" name="l00207"></a><span class="lineno">  207</span><span class="comment"> *   ~~~</span></div>
<div class="line"><a id="l00208" name="l00208"></a><span class="lineno">  208</span><span class="comment"> *   flow::async::Concurrent_task_loop L;</span></div>
<div class="line"><a id="l00209" name="l00209"></a><span class="lineno">  209</span><span class="comment"> *   auto op J = L.create_op(); // ATTN! The syntax is different from Strands but the idea is identical.</span></div>
<div class="line"><a id="l00210" name="l00210"></a><span class="lineno">  210</span><span class="comment"> *   ...</span></div>
<div class="line"><a id="l00211" name="l00211"></a><span class="lineno">  211</span><span class="comment"> *   X_type X(L.task_engine());</span></div>
<div class="line"><a id="l00212" name="l00212"></a><span class="lineno">  212</span><span class="comment"> *   // ATTN! The syntax is again somewhat different from bind_executor(S, F), but the idea is equivalent.</span></div>
<div class="line"><a id="l00213" name="l00213"></a><span class="lineno">  213</span><span class="comment"> *   X.async_A(&amp;A_target, A_settings, flow::async::asio_handler_via_op(&amp;L, J, F));</span></div>
<div class="line"><a id="l00214" name="l00214"></a><span class="lineno">  214</span><span class="comment"> *   ...</span></div>
<div class="line"><a id="l00215" name="l00215"></a><span class="lineno">  215</span><span class="comment"> *   Y_type Y(L.task_engine());</span></div>
<div class="line"><a id="l00216" name="l00216"></a><span class="lineno">  216</span><span class="comment"> *   Y.async_B(&amp;B_target, B_settings, flow::async::asio_handler_via_op(&amp;L, J, G));</span></div>
<div class="line"><a id="l00217" name="l00217"></a><span class="lineno">  217</span><span class="comment"> *   // X.sync_A() and Y.sync_B() are executing in background; F and G will run on respective completion;</span></div>
<div class="line"><a id="l00218" name="l00218"></a><span class="lineno">  218</span><span class="comment"> *   // but F() and G() shall run non-concurrently by virtue of being wrapped by the same Op: J.</span></div>
<div class="line"><a id="l00219" name="l00219"></a><span class="lineno">  219</span><span class="comment"> *   ~~~</span></div>
<div class="line"><a id="l00220" name="l00220"></a><span class="lineno">  220</span><span class="comment"> *</span></div>
<div class="line"><a id="l00221" name="l00221"></a><span class="lineno">  221</span><span class="comment"> * However, now that you&#39;re working with an I/O object directly, you must be careful.  Memorizing a `Task_engine`</span></div>
<div class="line"><a id="l00222" name="l00222"></a><span class="lineno">  222</span><span class="comment"> * at construction has different effects depending on which concrete subclass of Concurrent_task_loop `L` is.</span></div>
<div class="line"><a id="l00223" name="l00223"></a><span class="lineno">  223</span><span class="comment"> * Cross_thread_task_loop in particular will assign it to whichever thread is best.  Segregated_thread_task_loop</span></div>
<div class="line"><a id="l00224" name="l00224"></a><span class="lineno">  224</span><span class="comment"> * will keep using the same random-ish thread chosen when `L.task_engine()` is called.  If you need particular</span></div>
<div class="line"><a id="l00225" name="l00225"></a><span class="lineno">  225</span><span class="comment"> * behavior, you will need to strongly consider what to do: It is no longer totally generic behavior independent</span></div>
<div class="line"><a id="l00226" name="l00226"></a><span class="lineno">  226</span><span class="comment"> * of the subclass, as it generally is when it comes to the post() and `schedule_*()` APIs.</span></div>
<div class="line"><a id="l00227" name="l00227"></a><span class="lineno">  227</span><span class="comment"> *</span></div>
<div class="line"><a id="l00228" name="l00228"></a><span class="lineno">  228</span><span class="comment"> * Lastly, if you are going down that road (which may be fully necessary) then consider</span></div>
<div class="line"><a id="l00229" name="l00229"></a><span class="lineno">  229</span><span class="comment"> * the free function template op_to_exec_ctx() which is specialized</span></div>
<div class="line"><a id="l00230" name="l00230"></a><span class="lineno">  230</span><span class="comment"> * for each concrete Concurrent_task_loop; it takes a loop and an async::Op as input; and returns a boost.asio</span></div>
<div class="line"><a id="l00231" name="l00231"></a><span class="lineno">  231</span><span class="comment"> * &quot;execution context&quot; which can be passed -- much like a `Task_engine` in the above example -- to I/O object</span></div>
<div class="line"><a id="l00232" name="l00232"></a><span class="lineno">  232</span><span class="comment"> * constructors.  See the specializations -- as of this writing near Cross_thread_task_loop (returns util::Strand) and</span></div>
<div class="line"><a id="l00233" name="l00233"></a><span class="lineno">  233</span><span class="comment"> * Segregated_thread_task_loop (returns util::Task_engine) at least.  Choose between the above technique</span></div>
<div class="line"><a id="l00234" name="l00234"></a><span class="lineno">  234</span><span class="comment"> * and op_to_exec_ctx() when working directly with a boost.asio-compatible I/O object.</span></div>
<div class="line"><a id="l00235" name="l00235"></a><span class="lineno">  235</span><span class="comment"> *</span></div>
<div class="line"><a id="l00236" name="l00236"></a><span class="lineno">  236</span><span class="comment"> * I am self-conscious at the length and seeming complexity of this formal writeup but must emphasize: This is</span></div>
<div class="line"><a id="l00237" name="l00237"></a><span class="lineno">  237</span><span class="comment"> * using the same patterns as boost.asio users use.  It&#39;s just a matter of mapping them to `flow::async` Flow module&#39;s</span></div>
<div class="line"><a id="l00238" name="l00238"></a><span class="lineno">  238</span><span class="comment"> * generalized Concurrent_task_loop and async::Op APIs.  Reminder: The benefit of this is that one uses</span></div>
<div class="line"><a id="l00239" name="l00239"></a><span class="lineno">  239</span><span class="comment"> * boost.asio-equivalent semantics; yet the Concurrent_task_loop concrete subclass can implement it internally in</span></div>
<div class="line"><a id="l00240" name="l00240"></a><span class="lineno">  240</span><span class="comment"> * various ways that are or *aren&#39;t* what a direct use of `Task_engine` would do.  However, when using</span></div>
<div class="line"><a id="l00241" name="l00241"></a><span class="lineno">  241</span><span class="comment"> * I/O objects -- as opposed to post() -- the genericness will be less generic.  That is sometimes necessary.</span></div>
<div class="line"><a id="l00242" name="l00242"></a><span class="lineno">  242</span><span class="comment"> *</span></div>
<div class="line"><a id="l00243" name="l00243"></a><span class="lineno">  243</span><span class="comment"> * TL;DR: Any boost.asio-style (whether from boost.asio itself or custom) I/O object is to be used as normal, but:</span></div>
<div class="line"><a id="l00244" name="l00244"></a><span class="lineno">  244</span><span class="comment"> * To get a `Task_engine`, use task_engine().  To get a `Strand`-like thing util::Op, use create_op().</span></div>
<div class="line"><a id="l00245" name="l00245"></a><span class="lineno">  245</span><span class="comment"> * To *use* the `Strand`-like thing util::Op, use asio_handler_via_op().  Alternatively use actual `Task_engine`s or</span></div>
<div class="line"><a id="l00246" name="l00246"></a><span class="lineno">  246</span><span class="comment"> * `Strand`s directly if necessary; see op_to_exec_ctx() specializations for that purpose.</span></div>
<div class="line"><a id="l00247" name="l00247"></a><span class="lineno">  247</span><span class="comment"> * Lastly, make sure you understand the exact boost.asio behavior when using task_engine() (yields util::Task_engine),</span></div>
<div class="line"><a id="l00248" name="l00248"></a><span class="lineno">  248</span><span class="comment"> * asio_handler_via_op() (yields a util::Strand-bound callback), and/or op_to_exec_ctx() (yields a</span></div>
<div class="line"><a id="l00249" name="l00249"></a><span class="lineno">  249</span><span class="comment"> * util::Task_engine, util::Strand, or something else depending on subclass, to be passed as an &quot;execution context&quot;</span></div>
<div class="line"><a id="l00250" name="l00250"></a><span class="lineno">  250</span><span class="comment"> * to I/O object ctor).</span></div>
<div class="line"><a id="l00251" name="l00251"></a><span class="lineno">  251</span><span class="comment"> *</span></div>
<div class="line"><a id="l00252" name="l00252"></a><span class="lineno">  252</span><span class="comment"> * ### Are non-async boost.asio actions supported? ###</span></div>
<div class="line"><a id="l00253" name="l00253"></a><span class="lineno">  253</span><span class="comment"> * boost.asio `async_*()` actions are supported by `flow::async` module.  What about synchronous and non-blocking</span></div>
<div class="line"><a id="l00254" name="l00254"></a><span class="lineno">  254</span><span class="comment"> * operations?  Well, sure, they&#39;re supported.  This module is just not *about* them, hence the name.</span></div>
<div class="line"><a id="l00255" name="l00255"></a><span class="lineno">  255</span><span class="comment"> * Just for perspective though:</span></div>
<div class="line"><a id="l00256" name="l00256"></a><span class="lineno">  256</span><span class="comment"> *   - A non-blocking op (achieved in boost.asio normally by calling `something.non_blocking(true);` and then</span></div>
<div class="line"><a id="l00257" name="l00257"></a><span class="lineno">  257</span><span class="comment"> *     `some_op(something, ...)` or `something.some_op()`) can certainly be used whenever you want, in a task or</span></div>
<div class="line"><a id="l00258" name="l00258"></a><span class="lineno">  258</span><span class="comment"> *     outside of it, assuming of course you&#39;re not breaking thread-safety rules on concurrent access to `something`.</span></div>
<div class="line"><a id="l00259" name="l00259"></a><span class="lineno">  259</span><span class="comment"> *     The only &quot;connection&quot; to Concurrent_task_loop is that the `something` may be associated with</span></div>
<div class="line"><a id="l00260" name="l00260"></a><span class="lineno">  260</span><span class="comment"> *     `*(this-&gt;task_engine())`.  That&#39;s fine.</span></div>
<div class="line"><a id="l00261" name="l00261"></a><span class="lineno">  261</span><span class="comment"> *   - A blocking op (achieved by calling `something.non_blocking(false);` and then same as in previous bullet)</span></div>
<div class="line"><a id="l00262" name="l00262"></a><span class="lineno">  262</span><span class="comment"> *     can also be used whenever.  In some ways it&#39;s even less connected to Concurrent_task_loop, as blocking ops</span></div>
<div class="line"><a id="l00263" name="l00263"></a><span class="lineno">  263</span><span class="comment"> *     are only tangentially related to `Task_engine` in the first place; they don&#39;t participate in the</span></div>
<div class="line"><a id="l00264" name="l00264"></a><span class="lineno">  264</span><span class="comment"> *     internal event loop and simply usually call some blocking OS API or similar.  However, a blocking call</span></div>
<div class="line"><a id="l00265" name="l00265"></a><span class="lineno">  265</span><span class="comment"> *     does *block* the thread; so if you do this inside a `*this`-posted task, then that task will block.</span></div>
<div class="line"><a id="l00266" name="l00266"></a><span class="lineno">  266</span><span class="comment"> *     - Informally: It it best not to mix blocking and non-blocking tasks in the same Concurrent_task_loop.</span></div>
<div class="line"><a id="l00267" name="l00267"></a><span class="lineno">  267</span><span class="comment"> *       The blocking ones will harm the scheduler&#39;s ability to efficiently schedule the quick (non-blocking) tasks.</span></div>
<div class="line"><a id="l00268" name="l00268"></a><span class="lineno">  268</span><span class="comment"> *     - Informally: However, it is entirely reasonable and practical to limit a given Concurrent_task_loop</span></div>
<div class="line"><a id="l00269" name="l00269"></a><span class="lineno">  269</span><span class="comment"> *       (even, or especially, a multi-thread one) to blocking tasks exclusively.</span></div>
<div class="line"><a id="l00270" name="l00270"></a><span class="lineno">  270</span><span class="comment"> *       - One practical example is a multi-threaded</span></div>
<div class="line"><a id="l00271" name="l00271"></a><span class="lineno">  271</span><span class="comment"> *         DNS host resolver that maintains many threads performing blocking `getaddrinfo()` calls, since an async</span></div>
<div class="line"><a id="l00272" name="l00272"></a><span class="lineno">  272</span><span class="comment"> *         DNS API is not available; and a separate async-only loop/thread kicking off result-emitting handlers to the</span></div>
<div class="line"><a id="l00273" name="l00273"></a><span class="lineno">  273</span><span class="comment"> *         user, with the former blocking-only loop posting result-emitting tasks onto the async-only loop/thread.</span></div>
<div class="line"><a id="l00274" name="l00274"></a><span class="lineno">  274</span><span class="comment"> *         (boost.asio&#39;s out-of-the-box `resolver` provides an async API but is internally single-threaded and therefore</span></div>
<div class="line"><a id="l00275" name="l00275"></a><span class="lineno">  275</span><span class="comment"> *         unsuitable at scale.)</span></div>
<div class="line"><a id="l00276" name="l00276"></a><span class="lineno">  276</span><span class="comment"> *</span></div>
<div class="line"><a id="l00277" name="l00277"></a><span class="lineno">  277</span><span class="comment"> * @internal</span></div>
<div class="line"><a id="l00278" name="l00278"></a><span class="lineno">  278</span><span class="comment"> *</span></div>
<div class="line"><a id="l00279" name="l00279"></a><span class="lineno">  279</span><span class="comment"> * ### Design discussion re. Concurrent_task_loop hierarchy ###</span></div>
<div class="line"><a id="l00280" name="l00280"></a><span class="lineno">  280</span><span class="comment"> *</span></div>
<div class="line"><a id="l00281" name="l00281"></a><span class="lineno">  281</span><span class="comment"> * @see Task_qing_thread, particularly the constructor Task_qing_thread::Task_qing_thread() doc header, explaining</span></div>
<div class="line"><a id="l00282" name="l00282"></a><span class="lineno">  282</span><span class="comment"> *      how the Concurrent_task_loop hierarchy is an encapsulation of `vector&lt;Task_qing_thread&gt;`, arranged in various</span></div>
<div class="line"><a id="l00283" name="l00283"></a><span class="lineno">  283</span><span class="comment"> *      potential ways of working with each other.  It also includes an intro to the question of how to choose</span></div>
<div class="line"><a id="l00284" name="l00284"></a><span class="lineno">  284</span><span class="comment"> *      Cross_thread_task_loop vs. Segregated_thread_task_loop, at a lower level.</span></div>
<div class="line"><a id="l00285" name="l00285"></a><span class="lineno">  285</span><span class="comment"> *</span></div>
<div class="line"><a id="l00286" name="l00286"></a><span class="lineno">  286</span><span class="comment"> * While it is a clean interface, realistically speaking the entire existing hierarchy is perhaps best explained</span></div>
<div class="line"><a id="l00287" name="l00287"></a><span class="lineno">  287</span><span class="comment"> * by immediately discussing the 2 concrete classes the API as of this writing.  (More classes may well be added, but</span></div>
<div class="line"><a id="l00288" name="l00288"></a><span class="lineno">  288</span><span class="comment"> * as of this writing and probably for posterity it makes sense to discuss these 2 specific ones.)  The available pool</span></div>
<div class="line"><a id="l00289" name="l00289"></a><span class="lineno">  289</span><span class="comment"> * types are:</span></div>
<div class="line"><a id="l00290" name="l00290"></a><span class="lineno">  290</span><span class="comment"> *</span></div>
<div class="line"><a id="l00291" name="l00291"></a><span class="lineno">  291</span><span class="comment"> * - Cross_thread_task_loop: Internally, a single shared Task_engine and N `Task_qing_thread`s working together</span></div>
<div class="line"><a id="l00292" name="l00292"></a><span class="lineno">  292</span><span class="comment"> *   off that `post()`-capable engine.  N can be specified directly, or it can be auto-determined based on available</span></div>
<div class="line"><a id="l00293" name="l00293"></a><span class="lineno">  293</span><span class="comment"> *   hardware.  The latter will also enable automatically pinning the threads in such a way as to attempt to minimize</span></div>
<div class="line"><a id="l00294" name="l00294"></a><span class="lineno">  294</span><span class="comment"> *   latency, namely avoiding hyper-threading or other physical core sharing by several hardware threads; this is done</span></div>
<div class="line"><a id="l00295" name="l00295"></a><span class="lineno">  295</span><span class="comment"> *   by making N = # of physical cores; and pinning each software thread to a distinct group of logical cores (hardware</span></div>
<div class="line"><a id="l00296" name="l00296"></a><span class="lineno">  296</span><span class="comment"> *   threads), so that each software thread gets its own physical core, avoiding latency-increasing &quot;competition.&quot;</span></div>
<div class="line"><a id="l00297" name="l00297"></a><span class="lineno">  297</span><span class="comment"> *   An attempt is also made (achievable in Linux) to pin them in a consistent way, so that if another pool elsewhere</span></div>
<div class="line"><a id="l00298" name="l00298"></a><span class="lineno">  298</span><span class="comment"> *   uses the same code and config, they will arrange their same N threads in the same order.  This can help if thread i</span></div>
<div class="line"><a id="l00299" name="l00299"></a><span class="lineno">  299</span><span class="comment"> *   from pool 1 is producer writing to some area in memory, while thread i from pool 2 is consumer of same, reading</span></div>
<div class="line"><a id="l00300" name="l00300"></a><span class="lineno">  300</span><span class="comment"> *   there.  The `Cross_thread` part means that each multi-task sequence of callbacks constituting an async::Op, s/t</span></div>
<div class="line"><a id="l00301" name="l00301"></a><span class="lineno">  301</span><span class="comment"> *   those callbacks must not execute concurrently, may use more than 1 thread (internally, via the boost.asio</span></div>
<div class="line"><a id="l00302" name="l00302"></a><span class="lineno">  302</span><span class="comment"> *   util::Strand mechanism) which theoretically can improve use of thread time with asymmetrical load.  It might</span></div>
<div class="line"><a id="l00303" name="l00303"></a><span class="lineno">  303</span><span class="comment"> *   also negate per-thread cache locality, etc., and counter-act the effectiveness of aforementioned pinning.</span></div>
<div class="line"><a id="l00304" name="l00304"></a><span class="lineno">  304</span><span class="comment"> *   - `Cross_thread` means cross-thread.</span></div>
<div class="line"><a id="l00305" name="l00305"></a><span class="lineno">  305</span><span class="comment"> *</span></div>
<div class="line"><a id="l00306" name="l00306"></a><span class="lineno">  306</span><span class="comment"> * - Segregated_thread_task_loop: Internally, N `Task_qing_thread`s working together, each with its *own*</span></div>
<div class="line"><a id="l00307" name="l00307"></a><span class="lineno">  307</span><span class="comment"> *   `post()`-capable Task_engine queue, meaning by contrast with</span></div>
<div class="line"><a id="l00308" name="l00308"></a><span class="lineno">  308</span><span class="comment"> *   Cross_thread_task_loop a given `Op` always executes its tasks on the same thread.  Otherwise it works the same.</span></div>
<div class="line"><a id="l00309" name="l00309"></a><span class="lineno">  309</span><span class="comment"> *   Under asymmetrical load it might not use all available cross-thread time; however, it arguably also works</span></div>
<div class="line"><a id="l00310" name="l00310"></a><span class="lineno">  310</span><span class="comment"> *   straightforwardly &quot;synergistically&quot; with any attempts at per-processor-core pinning.</span></div>
<div class="line"><a id="l00311" name="l00311"></a><span class="lineno">  311</span><span class="comment"> *</span></div>
<div class="line"><a id="l00312" name="l00312"></a><span class="lineno">  312</span><span class="comment"> * The use is, of course, identical via the common API Concurrent_task_loop.</span></div>
<div class="line"><a id="l00313" name="l00313"></a><span class="lineno">  313</span><span class="comment"> *</span></div>
<div class="line"><a id="l00314" name="l00314"></a><span class="lineno">  314</span><span class="comment"> * Apologies for the conversational comment.  The internal subtleties are encapsulated and hidden from user.  Yet there</span></div>
<div class="line"><a id="l00315" name="l00315"></a><span class="lineno">  315</span><span class="comment"> * is considerable flexibility available.  One can think of this as a convenient wrapper around various functionality</span></div>
<div class="line"><a id="l00316" name="l00316"></a><span class="lineno">  316</span><span class="comment"> * typically used manually and separately from each other -- simplifying the core interface to just async::Op and</span></div>
<div class="line"><a id="l00317" name="l00317"></a><span class="lineno">  317</span><span class="comment"> * post() and providing automatic flexibility as to what functionality is in fact used and when as a result.</span></div>
<div class="line"><a id="l00318" name="l00318"></a><span class="lineno">  318</span><span class="comment"> * The functionality accessible: `post(Task_engine&amp;)`; scheduling via util::Strand; scheduling on specific thread;</span></div>
<div class="line"><a id="l00319" name="l00319"></a><span class="lineno">  319</span><span class="comment"> * non-concurrency guarantees of 2+ tasks in one async op; and thread-count selection and pinning based on available</span></div>
<div class="line"><a id="l00320" name="l00320"></a><span class="lineno">  320</span><span class="comment"> * processor architecture (hardware threads, physical cores).</span></div>
<div class="line"><a id="l00321" name="l00321"></a><span class="lineno">  321</span><span class="comment"> */</span></div>
<div class="line"><a id="l00322" name="l00322"></a><span class="lineno"><a class="line" href="classflow_1_1async_1_1Concurrent__task__loop.html">  322</a></span><span class="keyword">class </span><a class="code hl_class" href="classflow_1_1async_1_1Concurrent__task__loop.html">Concurrent_task_loop</a> :</div>
<div class="line"><a id="l00323" name="l00323"></a><span class="lineno">  323</span>  <span class="keyword">public</span> <a class="code hl_class" href="classflow_1_1util_1_1Null__interface.html">util::Null_interface</a></div>
<div class="line"><a id="l00324" name="l00324"></a><span class="lineno">  324</span>{</div>
<div class="line"><a id="l00325" name="l00325"></a><span class="lineno">  325</span><span class="keyword">public</span>:</div>
<div class="line"><a id="l00326" name="l00326"></a><span class="lineno">  326</span>  <span class="comment">// Types.</span></div>
<div class="line"><a id="l00327" name="l00327"></a><span class="lineno">  327</span><span class="comment"></span> </div>
<div class="line"><a id="l00328" name="l00328"></a><span class="lineno">  328</span><span class="comment">  /// Short-hand for the thread-initializer-function optional arg type to start().</span></div>
<div class="line"><a id="l00329" name="l00329"></a><span class="lineno"><a class="line" href="classflow_1_1async_1_1Concurrent__task__loop.html#aa164fb1fe1b3d7fce0de0174d77ea396">  329</a></span><span class="comment"></span>  <span class="keyword">using </span><a class="code hl_class" href="classflow_1_1Function.html">Thread_init_func</a> = <a class="code hl_class" href="classflow_1_1Function.html">Function</a>&lt;void (<span class="keywordtype">size_t</span> thread_idx)&gt;;</div>
<div class="line"><a id="l00330" name="l00330"></a><span class="lineno">  330</span> </div>
<div class="line"><a id="l00331" name="l00331"></a><span class="lineno">  331</span>  <span class="comment">// Constructors/destructor.</span></div>
<div class="line"><a id="l00332" name="l00332"></a><span class="lineno">  332</span><span class="comment"></span> </div>
<div class="line"><a id="l00333" name="l00333"></a><span class="lineno">  333</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00334" name="l00334"></a><span class="lineno">  334</span><span class="comment">   * Any implementing subclass&#39;s destructor shall execute stop() -- see its doc header please -- and then clean up</span></div>
<div class="line"><a id="l00335" name="l00335"></a><span class="lineno">  335</span><span class="comment">   * any resources.  The behavior of stop() has subtle implications, so please be sure to understand what it does.</span></div>
<div class="line"><a id="l00336" name="l00336"></a><span class="lineno">  336</span><span class="comment">   *</span></div>
<div class="line"><a id="l00337" name="l00337"></a><span class="lineno">  337</span><span class="comment">   * It is fine if stop() has already been called and returned.</span></div>
<div class="line"><a id="l00338" name="l00338"></a><span class="lineno">  338</span><span class="comment">   */</span></div>
<div class="line"><a id="l00339" name="l00339"></a><span class="lineno"><a class="line" href="classflow_1_1async_1_1Concurrent__task__loop.html#a7b9123d43e1cfae899b0e1bb52bb6dde">  339</a></span>  <a class="code hl_function" href="classflow_1_1async_1_1Concurrent__task__loop.html#a7b9123d43e1cfae899b0e1bb52bb6dde">~Concurrent_task_loop</a>() <span class="keyword">override</span>;</div>
<div class="line"><a id="l00340" name="l00340"></a><span class="lineno">  340</span> </div>
<div class="line"><a id="l00341" name="l00341"></a><span class="lineno">  341</span>  <span class="comment">// Methods.</span></div>
<div class="line"><a id="l00342" name="l00342"></a><span class="lineno">  342</span><span class="comment"></span> </div>
<div class="line"><a id="l00343" name="l00343"></a><span class="lineno">  343</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00344" name="l00344"></a><span class="lineno">  344</span><span class="comment">   * Starts all threads in the thread pool; any queued `post()`ed (and similar) tasks may begin executing immediately;</span></div>
<div class="line"><a id="l00345" name="l00345"></a><span class="lineno">  345</span><span class="comment">   * and any future posted work may execute in these threads.  Calling start() after start() is discouraged and may</span></div>
<div class="line"><a id="l00346" name="l00346"></a><span class="lineno">  346</span><span class="comment">   * log a WARNING but is a harmless no-op.  See also stop().</span></div>
<div class="line"><a id="l00347" name="l00347"></a><span class="lineno">  347</span><span class="comment">   *</span></div>
<div class="line"><a id="l00348" name="l00348"></a><span class="lineno">  348</span><span class="comment">   * The optional `init_task_or_empty` arg is a convenience thing.  It&#39;s equivalent to</span></div>
<div class="line"><a id="l00349" name="l00349"></a><span class="lineno">  349</span><span class="comment">   * `post(init_task_or_empty, Synchronicity::S_ASYNC_AND_AWAIT_CONCURRENT_COMPLETION)` executed upon return.</span></div>
<div class="line"><a id="l00350" name="l00350"></a><span class="lineno">  350</span><span class="comment">   * `init_task_or_empty()` will run in the new thread pool; and only once it `return`s, start() will `return`.</span></div>
<div class="line"><a id="l00351" name="l00351"></a><span class="lineno">  351</span><span class="comment">   * Rationale: It has come up in our experience several times that one wants to execute something in the new thread(s)</span></div>
<div class="line"><a id="l00352" name="l00352"></a><span class="lineno">  352</span><span class="comment">   * to initialize things, synchronously, before the main work -- various async `post()`ing and other calls -- can begin</span></div>
<div class="line"><a id="l00353" name="l00353"></a><span class="lineno">  353</span><span class="comment">   * in earnest.  Do note that any tasks enqueued before this start() but after the last stop() or constructor</span></div>
<div class="line"><a id="l00354" name="l00354"></a><span class="lineno">  354</span><span class="comment">   * may run first.</span></div>
<div class="line"><a id="l00355" name="l00355"></a><span class="lineno">  355</span><span class="comment">   *</span></div>
<div class="line"><a id="l00356" name="l00356"></a><span class="lineno">  356</span><span class="comment">   * Suppose a user-supplied task posted onto a worker thread throws an uncaught exception.  This will be handled</span></div>
<div class="line"><a id="l00357" name="l00357"></a><span class="lineno">  357</span><span class="comment">   * the same as if that occurred directly in that thread; in other words we don&#39;t catch it in any way, not even</span></div>
<div class="line"><a id="l00358" name="l00358"></a><span class="lineno">  358</span><span class="comment">   * to re-throw it or manually `std::abort()` or anything of that nature.  We informally recommend you handle uncaught</span></div>
<div class="line"><a id="l00359" name="l00359"></a><span class="lineno">  359</span><span class="comment">   * exceptions in a program-wide SIGABRT handler or equally program-wise custom `std::terminate()` (via</span></div>
<div class="line"><a id="l00360" name="l00360"></a><span class="lineno">  360</span><span class="comment">   * `std::set_terminate()`).  We informally recommend that all other threads similarly let any uncaught exception</span></div>
<div class="line"><a id="l00361" name="l00361"></a><span class="lineno">  361</span><span class="comment">   * fall through and deal with the fallout at the global program-wide level (to avoid losing precious stack trace</span></div>
<div class="line"><a id="l00362" name="l00362"></a><span class="lineno">  362</span><span class="comment">   * information).</span></div>
<div class="line"><a id="l00363" name="l00363"></a><span class="lineno">  363</span><span class="comment">   *</span></div>
<div class="line"><a id="l00364" name="l00364"></a><span class="lineno">  364</span><span class="comment">   * Assuming no such uncaught exception is thrown, all threads will run until stop() or the destructor runs and</span></div>
<div class="line"><a id="l00365" name="l00365"></a><span class="lineno">  365</span><span class="comment">   * returns.</span></div>
<div class="line"><a id="l00366" name="l00366"></a><span class="lineno">  366</span><span class="comment">   *</span></div>
<div class="line"><a id="l00367" name="l00367"></a><span class="lineno">  367</span><span class="comment">   * ### Thread safety ###</span></div>
<div class="line"><a id="l00368" name="l00368"></a><span class="lineno">  368</span><span class="comment">   * As noted in the class doc header, all methods are thread-safe on a common `*this` unless noted otherwise.</span></div>
<div class="line"><a id="l00369" name="l00369"></a><span class="lineno">  369</span><span class="comment">   * To wit: it is not safe to call `X.start()` concurrently with `X.start()` or with `X.stop()`.</span></div>
<div class="line"><a id="l00370" name="l00370"></a><span class="lineno">  370</span><span class="comment">   *</span></div>
<div class="line"><a id="l00371" name="l00371"></a><span class="lineno">  371</span><span class="comment">   * ### Thread initialization ###</span></div>
<div class="line"><a id="l00372" name="l00372"></a><span class="lineno">  372</span><span class="comment">   * Each thread start() starts shall be, soon, blocked by running an event loop (or part of a multi-thread event loop);</span></div>
<div class="line"><a id="l00373" name="l00373"></a><span class="lineno">  373</span><span class="comment">   * meaning it will be either blocking waiting for posted tasks/active events or executing posted tasks/event handlers.</span></div>
<div class="line"><a id="l00374" name="l00374"></a><span class="lineno">  374</span><span class="comment">   * It is, however, sometimes required to perform setup (usually of a low-level variety) in the thread before the</span></div>
<div class="line"><a id="l00375" name="l00375"></a><span class="lineno">  375</span><span class="comment">   * event loop proper begins.  (The use case that triggered this feature was wanting to execute Linux</span></div>
<div class="line"><a id="l00376" name="l00376"></a><span class="lineno">  376</span><span class="comment">   * `setns(CLONE_NEWNET)` to affect the subsequent socket-create calls in that thread.)  If needed: pass in</span></div>
<div class="line"><a id="l00377" name="l00377"></a><span class="lineno">  377</span><span class="comment">   * a non-empty function as `thread_init_func_or_empty` arg; it will receive the thread index 0, 1, ... as the arg.</span></div>
<div class="line"><a id="l00378" name="l00378"></a><span class="lineno">  378</span><span class="comment">   * It will run first-thing in the new thread.  Subtlety: As of this writing &quot;first-thing&quot; means literally first-thing;</span></div>
<div class="line"><a id="l00379" name="l00379"></a><span class="lineno">  379</span><span class="comment">   * it will run before any of the implementing start()&#39;s own code begins.  (This may be relaxed in the future to</span></div>
<div class="line"><a id="l00380" name="l00380"></a><span class="lineno">  380</span><span class="comment">   * merely &quot;before the event loop is ready for tasks.&quot;  Then this comment shall be updated.)</span></div>
<div class="line"><a id="l00381" name="l00381"></a><span class="lineno">  381</span><span class="comment">   *</span></div>
<div class="line"><a id="l00382" name="l00382"></a><span class="lineno">  382</span><span class="comment">   * Note: start() shall *block* until *all* `thread_init_func_or_empty()` invocations (if arg not `.empty()`)</span></div>
<div class="line"><a id="l00383" name="l00383"></a><span class="lineno">  383</span><span class="comment">   * have completed.  This can be important, for example, if the actions they are taking require elevated privileges,</span></div>
<div class="line"><a id="l00384" name="l00384"></a><span class="lineno">  384</span><span class="comment">   * then this guarantee means one can drop privileges after that.  Informally: we intuitively recommend against</span></div>
<div class="line"><a id="l00385" name="l00385"></a><span class="lineno">  385</span><span class="comment">   * blocking in this callback, although perhaps some use case might require it.  Just be careful.</span></div>
<div class="line"><a id="l00386" name="l00386"></a><span class="lineno">  386</span><span class="comment">   *</span></div>
<div class="line"><a id="l00387" name="l00387"></a><span class="lineno">  387</span><span class="comment">   * ### Design rationale (thread initialization arg) ###</span></div>
<div class="line"><a id="l00388" name="l00388"></a><span class="lineno">  388</span><span class="comment">   * Consider the specific implementation of the present interface, Segregated_thread_task_loop.  Something similar</span></div>
<div class="line"><a id="l00389" name="l00389"></a><span class="lineno">  389</span><span class="comment">   * to this feature is possible without this start() optional arg: One can simply post() onto each of the</span></div>
<div class="line"><a id="l00390" name="l00390"></a><span class="lineno">  390</span><span class="comment">   * per_thread_ops(), with Synchronicity::S_ASYNC_AND_AWAIT_CONCURRENT_COMPLETION.  It&#39;ll run as the first *task*</span></div>
<div class="line"><a id="l00391" name="l00391"></a><span class="lineno">  391</span><span class="comment">   * in each thread, as opposed to strictly-speaking first-*thing*, but it&#39;s close enough.  So why add this to the</span></div>
<div class="line"><a id="l00392" name="l00392"></a><span class="lineno">  392</span><span class="comment">   * interface?  Well, consider the other implementation, Cross_thread_task_loop.  By definition it&#39;s not possible</span></div>
<div class="line"><a id="l00393" name="l00393"></a><span class="lineno">  393</span><span class="comment">   * to target individual threads in that guy (per_thread_ops() exists but its `Op`s are *per*-thread, not *in*-thread;</span></div>
<div class="line"><a id="l00394" name="l00394"></a><span class="lineno">  394</span><span class="comment">   * they are `Strand`s, not threads).  So then some other, Cross_thread_task_loop-*only* API would be necessary to</span></div>
<div class="line"><a id="l00395" name="l00395"></a><span class="lineno">  395</span><span class="comment">   * get what we need.  Hence it made sense to add this as an interface-level feature.  Then these asymmetries go away</span></div>
<div class="line"><a id="l00396" name="l00396"></a><span class="lineno">  396</span><span class="comment">   * naturally.</span></div>
<div class="line"><a id="l00397" name="l00397"></a><span class="lineno">  397</span><span class="comment">   *</span></div>
<div class="line"><a id="l00398" name="l00398"></a><span class="lineno">  398</span><span class="comment">   * @todo Concurrent_task_loop::start() has an optional thread-initializer-function arg; it could be reasonable to</span></div>
<div class="line"><a id="l00399" name="l00399"></a><span class="lineno">  399</span><span class="comment">   * ass a thread-finalizer-function arg symmetrically.  As of this writing there is no use case, but it&#39;s certainly</span></div>
<div class="line"><a id="l00400" name="l00400"></a><span class="lineno">  400</span><span class="comment">   * conceivable.</span></div>
<div class="line"><a id="l00401" name="l00401"></a><span class="lineno">  401</span><span class="comment">   *</span></div>
<div class="line"><a id="l00402" name="l00402"></a><span class="lineno">  402</span><span class="comment">   * @param init_task_or_empty</span></div>
<div class="line"><a id="l00403" name="l00403"></a><span class="lineno">  403</span><span class="comment">   *        Ignored if `.empty()` (the default).  Otherwise `init_task_or_empty()` shall execute in one of the</span></div>
<div class="line"><a id="l00404" name="l00404"></a><span class="lineno">  404</span><span class="comment">   *        threads started by this method, delaying the method&#39;s return to the caller until `init_task_or_empty()`</span></div>
<div class="line"><a id="l00405" name="l00405"></a><span class="lineno">  405</span><span class="comment">   *        returns in said spawned thread.</span></div>
<div class="line"><a id="l00406" name="l00406"></a><span class="lineno">  406</span><span class="comment">   * @param thread_init_func_or_empty</span></div>
<div class="line"><a id="l00407" name="l00407"></a><span class="lineno">  407</span><span class="comment">   *        If not `.empty() == true`, `thread_init_func_or_empty(thread_idx)` shall be executed first-thing</span></div>
<div class="line"><a id="l00408" name="l00408"></a><span class="lineno">  408</span><span class="comment">   *        in each thread, for all `thread_idx` in [0, n_threads()).  start() will return no sooner than</span></div>
<div class="line"><a id="l00409" name="l00409"></a><span class="lineno">  409</span><span class="comment">   *        when each such callback has finished.</span></div>
<div class="line"><a id="l00410" name="l00410"></a><span class="lineno">  410</span><span class="comment">   */</span></div>
<div class="line"><a id="l00411" name="l00411"></a><span class="lineno"><a class="line" href="classflow_1_1async_1_1Concurrent__task__loop.html#afff5e62840791b309e178c5ddc26e594">  411</a></span>  <span class="keyword">virtual</span> <span class="keywordtype">void</span> <a class="code hl_function" href="classflow_1_1async_1_1Concurrent__task__loop.html#afff5e62840791b309e178c5ddc26e594">start</a>(<a class="code hl_class" href="classflow_1_1Function.html">Task</a>&amp;&amp; init_task_or_empty = <a class="code hl_typedef" href="namespaceflow_1_1async.html#af35fb65bdea1a3a92929ec2c4a6a6b72">Task</a>(),</div>
<div class="line"><a id="l00412" name="l00412"></a><span class="lineno">  412</span>                     <span class="keyword">const</span> <a class="code hl_class" href="classflow_1_1Function.html">Thread_init_func</a>&amp; thread_init_func_or_empty = <a class="code hl_typedef" href="classflow_1_1async_1_1Concurrent__task__loop.html#aa164fb1fe1b3d7fce0de0174d77ea396">Thread_init_func</a>()) = 0;</div>
<div class="line"><a id="l00413" name="l00413"></a><span class="lineno">  413</span><span class="comment"></span> </div>
<div class="line"><a id="l00414" name="l00414"></a><span class="lineno">  414</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00415" name="l00415"></a><span class="lineno">  415</span><span class="comment">   * Waits for any ongoing task(s)/completion handler(s) to return; then prevents any further-queued such tasks</span></div>
<div class="line"><a id="l00416" name="l00416"></a><span class="lineno">  416</span><span class="comment">   * from running; then gracefully stops/joins all threads in pool; and then returns.  The post-condition is that</span></div>
<div class="line"><a id="l00417" name="l00417"></a><span class="lineno">  417</span><span class="comment">   * the worker threads have fully and gracefully exited.</span></div>
<div class="line"><a id="l00418" name="l00418"></a><span class="lineno">  418</span><span class="comment">   *</span></div>
<div class="line"><a id="l00419" name="l00419"></a><span class="lineno">  419</span><span class="comment">   * Upon return from this method, any further `post()` or more complex async ops can safely be invoked -- but they</span></div>
<div class="line"><a id="l00420" name="l00420"></a><span class="lineno">  420</span><span class="comment">   * will not do any actual work, and no tasks or completion handlers will run until start().  In particular</span></div>
<div class="line"><a id="l00421" name="l00421"></a><span class="lineno">  421</span><span class="comment">   * task_engine() will still return a util::Task_engine, and one can still invoke `post()` and async I/O ops on it:</span></div>
<div class="line"><a id="l00422" name="l00422"></a><span class="lineno">  422</span><span class="comment">   * doing so won&#39;t crash, but it won&#39;t do the requested work until start(). (Recall that there are no more</span></div>
<div class="line"><a id="l00423" name="l00423"></a><span class="lineno">  423</span><span class="comment">   * threads in which to do this work.)  The destructor can then be invoked, at which point obviously one cannot</span></div>
<div class="line"><a id="l00424" name="l00424"></a><span class="lineno">  424</span><span class="comment">   * `post()` (or anything else like it) either.</span></div>
<div class="line"><a id="l00425" name="l00425"></a><span class="lineno">  425</span><span class="comment">   *</span></div>
<div class="line"><a id="l00426" name="l00426"></a><span class="lineno">  426</span><span class="comment">   * This condition is reversible via start().  In fact, `*this` starts in the stopped state, and start() is required</span></div>
<div class="line"><a id="l00427" name="l00427"></a><span class="lineno">  427</span><span class="comment">   * to make posted tasks actually execute.</span></div>
<div class="line"><a id="l00428" name="l00428"></a><span class="lineno">  428</span><span class="comment">   *</span></div>
<div class="line"><a id="l00429" name="l00429"></a><span class="lineno">  429</span><span class="comment">   * Lastly, calling stop() after stop() returns is a harmless no-op.  Also note the destructor shall call stop().</span></div>
<div class="line"><a id="l00430" name="l00430"></a><span class="lineno">  430</span><span class="comment">   *</span></div>
<div class="line"><a id="l00431" name="l00431"></a><span class="lineno">  431</span><span class="comment">   * ### Thread safety ###</span></div>
<div class="line"><a id="l00432" name="l00432"></a><span class="lineno">  432</span><span class="comment">   * As noted in the class doc header, all methods are thread-safe on a common `*this` unless noted otherwise.</span></div>
<div class="line"><a id="l00433" name="l00433"></a><span class="lineno">  433</span><span class="comment">   * To wit: it is not safe to call `X.stop()` concurrently with `X.stop()` or with `X.start()`.</span></div>
<div class="line"><a id="l00434" name="l00434"></a><span class="lineno">  434</span><span class="comment">   *</span></div>
<div class="line"><a id="l00435" name="l00435"></a><span class="lineno">  435</span><span class="comment">   * You may call stop() from within a task/completion handler executing within `*this` thread pool.  Of course</span></div>
<div class="line"><a id="l00436" name="l00436"></a><span class="lineno">  436</span><span class="comment">   * you may also do this from another thread.</span></div>
<div class="line"><a id="l00437" name="l00437"></a><span class="lineno">  437</span><span class="comment">   *</span></div>
<div class="line"><a id="l00438" name="l00438"></a><span class="lineno">  438</span><span class="comment">   * ### Rationale ###</span></div>
<div class="line"><a id="l00439" name="l00439"></a><span class="lineno">  439</span><span class="comment">   * This is similar to boost.asio `Task_engine::stop()`.  At a minimum it is useful, when shutting down the app</span></div>
<div class="line"><a id="l00440" name="l00440"></a><span class="lineno">  440</span><span class="comment">   * or module, in the situation where 2+ `Concurrent_task_loop`s routinely post work onto each other (or in at least 1</span></div>
<div class="line"><a id="l00441" name="l00441"></a><span class="lineno">  441</span><span class="comment">   * direction).  To safely stop all 2+ loops, one would first invoke this stop() method on each</span></div>
<div class="line"><a id="l00442" name="l00442"></a><span class="lineno">  442</span><span class="comment">   * Concurrent_task_loop, in any order; having done that destroy (invoke dtor on) each Concurrent_task_loop, also in</span></div>
<div class="line"><a id="l00443" name="l00443"></a><span class="lineno">  443</span><span class="comment">   * any order.  This way any cross-posting will safely work during the stop() phase (but do nothing on the</span></div>
<div class="line"><a id="l00444" name="l00444"></a><span class="lineno">  444</span><span class="comment">   * already-stopped loops); and by the time the destructor-invoking phase begins, no more cross-posting tasks can</span></div>
<div class="line"><a id="l00445" name="l00445"></a><span class="lineno">  445</span><span class="comment">   * possibly be executing (as their threads don&#39;t even exist by then).</span></div>
<div class="line"><a id="l00446" name="l00446"></a><span class="lineno">  446</span><span class="comment">   *</span></div>
<div class="line"><a id="l00447" name="l00447"></a><span class="lineno">  447</span><span class="comment">   * Note, however, that this is as graceful as we can generically guarantee -- in that it won&#39;t crash/lead to undefined</span></div>
<div class="line"><a id="l00448" name="l00448"></a><span class="lineno">  448</span><span class="comment">   * behavior on our account -- but it is up to you to ensure your algorithm is robust, in that nothing bad will happen</span></div>
<div class="line"><a id="l00449" name="l00449"></a><span class="lineno">  449</span><span class="comment">   * if tasks are suddenly prevented from running.  For example, if task A locks some file, while task B later unlocks</span></div>
<div class="line"><a id="l00450" name="l00450"></a><span class="lineno">  450</span><span class="comment">   * it, *you* are the one who must ensure you don&#39;t invoke stop() &quot;between&quot; task A and task B.  (E.g., invoking it</span></div>
<div class="line"><a id="l00451" name="l00451"></a><span class="lineno">  451</span><span class="comment">   * while A runs will let A complete; but it will very possibly prevent B from starting subsequently.)  We have no way</span></div>
<div class="line"><a id="l00452" name="l00452"></a><span class="lineno">  452</span><span class="comment">   * of knowing to let task B run first and only then stop the thread(s).</span></div>
<div class="line"><a id="l00453" name="l00453"></a><span class="lineno">  453</span><span class="comment">   *</span></div>
<div class="line"><a id="l00454" name="l00454"></a><span class="lineno">  454</span><span class="comment">   * Lastly, the stop() and start() mechanism is amenable to dynamically configuring thread behavior such as the</span></div>
<div class="line"><a id="l00455" name="l00455"></a><span class="lineno">  455</span><span class="comment">   * number of threads in the pool.</span></div>
<div class="line"><a id="l00456" name="l00456"></a><span class="lineno">  456</span><span class="comment">   *</span></div>
<div class="line"><a id="l00457" name="l00457"></a><span class="lineno">  457</span><span class="comment">   * @todo boost.asio has advanced features that might help to mark certain tasks as &quot;must-run if already queued, even</span></div>
<div class="line"><a id="l00458" name="l00458"></a><span class="lineno">  458</span><span class="comment">   * if one `stop()`s&quot;; consider providing user-friendly access to these features, perhaps in the context of the</span></div>
<div class="line"><a id="l00459" name="l00459"></a><span class="lineno">  459</span><span class="comment">   * existing Concurrent_task_loop::stop() API.  These features are documented as of this writing at least in the</span></div>
<div class="line"><a id="l00460" name="l00460"></a><span class="lineno">  460</span><span class="comment">   * `io_context` doc page.</span></div>
<div class="line"><a id="l00461" name="l00461"></a><span class="lineno">  461</span><span class="comment">   */</span></div>
<div class="line"><a id="l00462" name="l00462"></a><span class="lineno"><a class="line" href="classflow_1_1async_1_1Concurrent__task__loop.html#aadadb5b8b6c40ddc86c205de1b8f25b1">  462</a></span>  <span class="keyword">virtual</span> <span class="keywordtype">void</span> <a class="code hl_function" href="classflow_1_1async_1_1Concurrent__task__loop.html#aadadb5b8b6c40ddc86c205de1b8f25b1">stop</a>() = 0;</div>
<div class="line"><a id="l00463" name="l00463"></a><span class="lineno">  463</span><span class="comment"></span> </div>
<div class="line"><a id="l00464" name="l00464"></a><span class="lineno">  464</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00465" name="l00465"></a><span class="lineno">  465</span><span class="comment">   * How many threads does start() start?</span></div>
<div class="line"><a id="l00466" name="l00466"></a><span class="lineno">  466</span><span class="comment">   * @return See above.</span></div>
<div class="line"><a id="l00467" name="l00467"></a><span class="lineno">  467</span><span class="comment">   */</span></div>
<div class="line"><a id="l00468" name="l00468"></a><span class="lineno"><a class="line" href="classflow_1_1async_1_1Concurrent__task__loop.html#a131335863b19446dbc349de181d4b5a1">  468</a></span>  <span class="keyword">virtual</span> <span class="keywordtype">size_t</span> <a class="code hl_function" href="classflow_1_1async_1_1Concurrent__task__loop.html#a131335863b19446dbc349de181d4b5a1">n_threads</a>() <span class="keyword">const</span> = 0;</div>
<div class="line"><a id="l00469" name="l00469"></a><span class="lineno">  469</span><span class="comment"></span> </div>
<div class="line"><a id="l00470" name="l00470"></a><span class="lineno">  470</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00471" name="l00471"></a><span class="lineno">  471</span><span class="comment">   * Return a new Op which can bundle together an arbitrary set of `post()`s that would result in the</span></div>
<div class="line"><a id="l00472" name="l00472"></a><span class="lineno">  472</span><span class="comment">   * provided task functions executing non-concurrently.  That&#39;s informal; the formal semantics of what async::Op</span></div>
<div class="line"><a id="l00473" name="l00473"></a><span class="lineno">  473</span><span class="comment">   * means are in async::Op doc header.  Informally: please recall that a copy (of a copy, of a copy, ...) of</span></div>
<div class="line"><a id="l00474" name="l00474"></a><span class="lineno">  474</span><span class="comment">   * an `Op` is an equivalent `Op`, and copying them is light-weight (at worst like copying `shared_ptr`).</span></div>
<div class="line"><a id="l00475" name="l00475"></a><span class="lineno">  475</span><span class="comment">   *</span></div>
<div class="line"><a id="l00476" name="l00476"></a><span class="lineno">  476</span><span class="comment">   * All `Op`s shall remain valid throughout the lifetime of `*this`.</span></div>
<div class="line"><a id="l00477" name="l00477"></a><span class="lineno">  477</span><span class="comment">   *</span></div>
<div class="line"><a id="l00478" name="l00478"></a><span class="lineno">  478</span><span class="comment">   * This is the more general method of obtaining an async::Op, vs. going through per_thread_ops().</span></div>
<div class="line"><a id="l00479" name="l00479"></a><span class="lineno">  479</span><span class="comment">   * It should be used *unless* you specifically need to access some</span></div>
<div class="line"><a id="l00480" name="l00480"></a><span class="lineno">  480</span><span class="comment">   * per-thread resource in the associated `Task`s.  See class doc header for more discussion on this dichotomy.</span></div>
<div class="line"><a id="l00481" name="l00481"></a><span class="lineno">  481</span><span class="comment">   * TL;DR: Use create_op() by default, *unless* the `Task`s you plan to execute are working on some</span></div>
<div class="line"><a id="l00482" name="l00482"></a><span class="lineno">  482</span><span class="comment">   * per-thread resource.</span></div>
<div class="line"><a id="l00483" name="l00483"></a><span class="lineno">  483</span><span class="comment">   *</span></div>
<div class="line"><a id="l00484" name="l00484"></a><span class="lineno">  484</span><span class="comment">   * @return See above.</span></div>
<div class="line"><a id="l00485" name="l00485"></a><span class="lineno">  485</span><span class="comment">   */</span></div>
<div class="line"><a id="l00486" name="l00486"></a><span class="lineno"><a class="line" href="classflow_1_1async_1_1Concurrent__task__loop.html#a4ee1c5f5785af0bcc6aed0757981ffe3">  486</a></span>  <span class="keyword">virtual</span> <a class="code hl_typedef" href="namespaceflow_1_1async.html#a024042c64b7dc544a7a5587afa4b1949">Op</a> <a class="code hl_function" href="classflow_1_1async_1_1Concurrent__task__loop.html#a4ee1c5f5785af0bcc6aed0757981ffe3">create_op</a>() = 0;</div>
<div class="line"><a id="l00487" name="l00487"></a><span class="lineno">  487</span><span class="comment"></span> </div>
<div class="line"><a id="l00488" name="l00488"></a><span class="lineno">  488</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00489" name="l00489"></a><span class="lineno">  489</span><span class="comment">   * Returns the optional-use, pre-created collection of per-thread async::Op objects, such that</span></div>
<div class="line"><a id="l00490" name="l00490"></a><span class="lineno">  490</span><span class="comment">   * the i-th `Op` therein corresponds to the i-th (of N, where N = # of threads in this pool) thread.</span></div>
<div class="line"><a id="l00491" name="l00491"></a><span class="lineno">  491</span><span class="comment">   *</span></div>
<div class="line"><a id="l00492" name="l00492"></a><span class="lineno">  492</span><span class="comment">   * All `Op`s and this `Op_list&amp;` shall remain valid throughout the lifetime of `*this`.</span></div>
<div class="line"><a id="l00493" name="l00493"></a><span class="lineno">  493</span><span class="comment">   *</span></div>
<div class="line"><a id="l00494" name="l00494"></a><span class="lineno">  494</span><span class="comment">   * This is an advanced/legacy-ish feature.  Please see class doc header for discussion on when one should use this</span></div>
<div class="line"><a id="l00495" name="l00495"></a><span class="lineno">  495</span><span class="comment">   * as opposed to the simpler create_op().</span></div>
<div class="line"><a id="l00496" name="l00496"></a><span class="lineno">  496</span><span class="comment">   *</span></div>
<div class="line"><a id="l00497" name="l00497"></a><span class="lineno">  497</span><span class="comment">   * @return See above.</span></div>
<div class="line"><a id="l00498" name="l00498"></a><span class="lineno">  498</span><span class="comment">   */</span></div>
<div class="line"><a id="l00499" name="l00499"></a><span class="lineno"><a class="line" href="classflow_1_1async_1_1Concurrent__task__loop.html#a54bd938b133103328a90d50823755358">  499</a></span>  <span class="keyword">virtual</span> <span class="keyword">const</span> <a class="code hl_class" href="classflow_1_1async_1_1Op__list.html">Op_list</a>&amp; <a class="code hl_function" href="classflow_1_1async_1_1Concurrent__task__loop.html#a54bd938b133103328a90d50823755358">per_thread_ops</a>() = 0;</div>
<div class="line"><a id="l00500" name="l00500"></a><span class="lineno">  500</span><span class="comment"></span> </div>
<div class="line"><a id="l00501" name="l00501"></a><span class="lineno">  501</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00502" name="l00502"></a><span class="lineno">  502</span><span class="comment">   * Cause the given `Task` (function) to execute within the thread pool as soon as possible, in the first thread</span></div>
<div class="line"><a id="l00503" name="l00503"></a><span class="lineno">  503</span><span class="comment">   * available, in otherwise first-come-first-served fashion.  `task` may execute concurrently with some other `Task` if</span></div>
<div class="line"><a id="l00504" name="l00504"></a><span class="lineno">  504</span><span class="comment">   * there are 2+ threads in `*this` pool.  Meanings of &quot;as soon as possible&quot; and &quot;available&quot; are to be determined by</span></div>
<div class="line"><a id="l00505" name="l00505"></a><span class="lineno">  505</span><span class="comment">   * the concrete method implementation.  That is, the interface does not promise it&#39;ll use literally the first</span></div>
<div class="line"><a id="l00506" name="l00506"></a><span class="lineno">  506</span><span class="comment">   * thread to be idle, but informally -- all else being equal -- that&#39;s a great goal.</span></div>
<div class="line"><a id="l00507" name="l00507"></a><span class="lineno">  507</span><span class="comment">   *</span></div>
<div class="line"><a id="l00508" name="l00508"></a><span class="lineno">  508</span><span class="comment">   * `synchronicity` controls the precise behavior of the &quot;post&quot; operation.  Read #Synchronicity `enum` docs carefully.</span></div>
<div class="line"><a id="l00509" name="l00509"></a><span class="lineno">  509</span><span class="comment">   * That said: if left defaulted, `post()` works in the `post(Task_engine&amp;)` manner: return immediately; then</span></div>
<div class="line"><a id="l00510" name="l00510"></a><span class="lineno">  510</span><span class="comment">   * execute either concurrently in another thread or later in the same thread.</span></div>
<div class="line"><a id="l00511" name="l00511"></a><span class="lineno">  511</span><span class="comment">   *</span></div>
<div class="line"><a id="l00512" name="l00512"></a><span class="lineno">  512</span><span class="comment">   * This is safe to call after stop(), but `task()` will not run until start() (see stop() doc header).</span></div>
<div class="line"><a id="l00513" name="l00513"></a><span class="lineno">  513</span><span class="comment">   * Synchronicity::S_ASYNC_AND_AWAIT_CONCURRENT_COMPLETION and Synchronicity::S_ASYNC_AND_AWAIT_CONCURRENT_START modes</span></div>
<div class="line"><a id="l00514" name="l00514"></a><span class="lineno">  514</span><span class="comment">   * will, therefore, block infinitely in that case; so don&#39;t do that after stop().</span></div>
<div class="line"><a id="l00515" name="l00515"></a><span class="lineno">  515</span><span class="comment">   *</span></div>
<div class="line"><a id="l00516" name="l00516"></a><span class="lineno">  516</span><span class="comment">   * Reminder: This is thread-safe as explained in class doc header.</span></div>
<div class="line"><a id="l00517" name="l00517"></a><span class="lineno">  517</span><span class="comment">   *</span></div>
<div class="line"><a id="l00518" name="l00518"></a><span class="lineno">  518</span><span class="comment">   * ### Rationale note ###</span></div>
<div class="line"><a id="l00519" name="l00519"></a><span class="lineno">  519</span><span class="comment">   * The callback arg would normally be the last arg, by Flow coding style.  In this case it isn&#39;t, because</span></div>
<div class="line"><a id="l00520" name="l00520"></a><span class="lineno">  520</span><span class="comment">   * it is more valuable to make `synchronicity` optional (which it can only be if it&#39;s the last arg).</span></div>
<div class="line"><a id="l00521" name="l00521"></a><span class="lineno">  521</span><span class="comment">   *</span></div>
<div class="line"><a id="l00522" name="l00522"></a><span class="lineno">  522</span><span class="comment">   * @param task</span></div>
<div class="line"><a id="l00523" name="l00523"></a><span class="lineno">  523</span><span class="comment">   *        Task to execute.  `task` object itself may be `move`d and saved.</span></div>
<div class="line"><a id="l00524" name="l00524"></a><span class="lineno">  524</span><span class="comment">   * @param synchronicity</span></div>
<div class="line"><a id="l00525" name="l00525"></a><span class="lineno">  525</span><span class="comment">   *        Controls when `task()` will execute particularly in relation to when this `post()` call returns.</span></div>
<div class="line"><a id="l00526" name="l00526"></a><span class="lineno">  526</span><span class="comment">   */</span></div>
<div class="line"><a id="l00527" name="l00527"></a><span class="lineno"><a class="line" href="classflow_1_1async_1_1Concurrent__task__loop.html#a24f96f97ee24bfabb06c8609bc0e94a6">  527</a></span>  <span class="keyword">virtual</span> <span class="keywordtype">void</span> <a class="code hl_function" href="classflow_1_1async_1_1Concurrent__task__loop.html#a24f96f97ee24bfabb06c8609bc0e94a6">post</a>(<a class="code hl_class" href="classflow_1_1Function.html">Task</a>&amp;&amp; task, <a class="code hl_enumeration" href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485">Synchronicity</a> synchronicity = <a class="code hl_enumvalue" href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485a4d7a5700444c0570af37b1f9bcc6eb1f">Synchronicity::S_ASYNC</a>) = 0;</div>
<div class="line"><a id="l00528" name="l00528"></a><span class="lineno">  528</span><span class="comment"></span> </div>
<div class="line"><a id="l00529" name="l00529"></a><span class="lineno">  529</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00530" name="l00530"></a><span class="lineno">  530</span><span class="comment">   * Identical to the other post() with the added constraint that no other `Task` *also* similarly posted with the</span></div>
<div class="line"><a id="l00531" name="l00531"></a><span class="lineno">  531</span><span class="comment">   * equivalent async::Op may execute concurrently.  See doc header for async::Op for a formal definition of</span></div>
<div class="line"><a id="l00532" name="l00532"></a><span class="lineno">  532</span><span class="comment">   * what this call does w/r/t async::Op.</span></div>
<div class="line"><a id="l00533" name="l00533"></a><span class="lineno">  533</span><span class="comment">   *</span></div>
<div class="line"><a id="l00534" name="l00534"></a><span class="lineno">  534</span><span class="comment">   * Reminder: This is thread-safe as explained in class doc header.</span></div>
<div class="line"><a id="l00535" name="l00535"></a><span class="lineno">  535</span><span class="comment">   *</span></div>
<div class="line"><a id="l00536" name="l00536"></a><span class="lineno">  536</span><span class="comment">   * @param op</span></div>
<div class="line"><a id="l00537" name="l00537"></a><span class="lineno">  537</span><span class="comment">   *        The (presumably) multi-async-step operation to which `task` belongs, such that no `Task`s associated with</span></div>
<div class="line"><a id="l00538" name="l00538"></a><span class="lineno">  538</span><span class="comment">   *        `op` may execute concurrently with `task`.  If `op.empty()` (a/k/a `op == Op()`, recalling that `Op()`</span></div>
<div class="line"><a id="l00539" name="l00539"></a><span class="lineno">  539</span><span class="comment">   *        is null/sentinel), then `assert()` trips.</span></div>
<div class="line"><a id="l00540" name="l00540"></a><span class="lineno">  540</span><span class="comment">   * @param task</span></div>
<div class="line"><a id="l00541" name="l00541"></a><span class="lineno">  541</span><span class="comment">   *        See other post().</span></div>
<div class="line"><a id="l00542" name="l00542"></a><span class="lineno">  542</span><span class="comment">   * @param synchronicity</span></div>
<div class="line"><a id="l00543" name="l00543"></a><span class="lineno">  543</span><span class="comment">   *        See other post().</span></div>
<div class="line"><a id="l00544" name="l00544"></a><span class="lineno">  544</span><span class="comment">   */</span></div>
<div class="line"><a id="l00545" name="l00545"></a><span class="lineno"><a class="line" href="classflow_1_1async_1_1Concurrent__task__loop.html#ab0e31275441218c4d77df0730fd5e8f7">  545</a></span>  <span class="keyword">virtual</span> <span class="keywordtype">void</span> <a class="code hl_function" href="classflow_1_1async_1_1Concurrent__task__loop.html#ab0e31275441218c4d77df0730fd5e8f7">post</a>(<span class="keyword">const</span> <a class="code hl_typedef" href="namespaceflow_1_1async.html#a024042c64b7dc544a7a5587afa4b1949">Op</a>&amp; op, <a class="code hl_class" href="classflow_1_1Function.html">Task</a>&amp;&amp; task, <a class="code hl_enumeration" href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485">Synchronicity</a> synchronicity = <a class="code hl_enumvalue" href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485a4d7a5700444c0570af37b1f9bcc6eb1f">Synchronicity::S_ASYNC</a>) = 0;</div>
<div class="line"><a id="l00546" name="l00546"></a><span class="lineno">  546</span><span class="comment"></span> </div>
<div class="line"><a id="l00547" name="l00547"></a><span class="lineno">  547</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00548" name="l00548"></a><span class="lineno">  548</span><span class="comment">   * Equivalent to 2-argument post() but execution is scheduled for later, after the given time period passes.</span></div>
<div class="line"><a id="l00549" name="l00549"></a><span class="lineno">  549</span><span class="comment">   *</span></div>
<div class="line"><a id="l00550" name="l00550"></a><span class="lineno">  550</span><span class="comment">   * The semantics are, in all ways in which this differs from 2-argument post(), those of</span></div>
<div class="line"><a id="l00551" name="l00551"></a><span class="lineno">  551</span><span class="comment">   * util::schedule_task_from_now().  This includes the meaning of the returned value and the nature of</span></div>
<div class="line"><a id="l00552" name="l00552"></a><span class="lineno">  552</span><span class="comment">   * util::Scheduled_task.  Also, in particular, one can perform actions like canceling, short-firing, and</span></div>
<div class="line"><a id="l00553" name="l00553"></a><span class="lineno">  553</span><span class="comment">   * info-access by passing the returned handle into util::scheduled_task_cancel() and others.</span></div>
<div class="line"><a id="l00554" name="l00554"></a><span class="lineno">  554</span><span class="comment">   *</span></div>
<div class="line"><a id="l00555" name="l00555"></a><span class="lineno">  555</span><span class="comment">   * @warning If n_threads() is 1, then you *must* not call any `util::scheduled_task_*()` function on the returned</span></div>
<div class="line"><a id="l00556" name="l00556"></a><span class="lineno">  556</span><span class="comment">   *          handle except from within `*this` loop&#39;s tasks.</span></div>
<div class="line"><a id="l00557" name="l00557"></a><span class="lineno">  557</span><span class="comment">   *</span></div>
<div class="line"><a id="l00558" name="l00558"></a><span class="lineno">  558</span><span class="comment">   * @todo Deal with the scheduled-tasks-affected-from-outside-loop corner case of the</span></div>
<div class="line"><a id="l00559" name="l00559"></a><span class="lineno">  559</span><span class="comment">   *       `Concurrent_task_loop::schedule_*()` APIs.  Perhaps add `bool in_loop_use_only` arg</span></div>
<div class="line"><a id="l00560" name="l00560"></a><span class="lineno">  560</span><span class="comment">   *       which, if `false`, will always disable the `single_threaded` optimization internally.</span></div>
<div class="line"><a id="l00561" name="l00561"></a><span class="lineno">  561</span><span class="comment">   *       At this time it always enables it if `n_threads() == 1` which will cause thread un-safety if</span></div>
<div class="line"><a id="l00562" name="l00562"></a><span class="lineno">  562</span><span class="comment">   *       the returned handle is touched from outside an in-loop task.  `void` versions of the `schedule_*()` APIs</span></div>
<div class="line"><a id="l00563" name="l00563"></a><span class="lineno">  563</span><span class="comment">   *       should be added which would lack this, as in that case there is no handle to misuse outside the loop.</span></div>
<div class="line"><a id="l00564" name="l00564"></a><span class="lineno">  564</span><span class="comment">   *</span></div>
<div class="line"><a id="l00565" name="l00565"></a><span class="lineno">  565</span><span class="comment">   * @param from_now</span></div>
<div class="line"><a id="l00566" name="l00566"></a><span class="lineno">  566</span><span class="comment">   *        See util::schedule_task_from_now().</span></div>
<div class="line"><a id="l00567" name="l00567"></a><span class="lineno">  567</span><span class="comment">   * @param task</span></div>
<div class="line"><a id="l00568" name="l00568"></a><span class="lineno">  568</span><span class="comment">   *        The task to execute within `*this` unless successfully canceled.</span></div>
<div class="line"><a id="l00569" name="l00569"></a><span class="lineno">  569</span><span class="comment">   *        `task` object itself may be `move`d and saved.</span></div>
<div class="line"><a id="l00570" name="l00570"></a><span class="lineno">  570</span><span class="comment">   * @return See util::schedule_task_from_now().</span></div>
<div class="line"><a id="l00571" name="l00571"></a><span class="lineno">  571</span><span class="comment">   */</span></div>
<div class="line"><a id="l00572" name="l00572"></a><span class="lineno"><a class="line" href="classflow_1_1async_1_1Concurrent__task__loop.html#ac6b98b440d52c079c22d7972c9b12e1b">  572</a></span>  <span class="keyword">virtual</span> <a class="code hl_typedef" href="namespaceflow_1_1util.html#aa0d10f5a906b3229f48979aa43e9ff7e">util::Scheduled_task_handle</a> <a class="code hl_function" href="classflow_1_1async_1_1Concurrent__task__loop.html#ac6b98b440d52c079c22d7972c9b12e1b">schedule_from_now</a>(<span class="keyword">const</span> <a class="code hl_typedef" href="namespaceflow.html#a48799f1263cdeedec125be51a3db2b79">Fine_duration</a>&amp; from_now, <a class="code hl_class" href="classflow_1_1Function.html">Scheduled_task</a>&amp;&amp; task) = 0;</div>
<div class="line"><a id="l00573" name="l00573"></a><span class="lineno">  573</span><span class="comment"></span> </div>
<div class="line"><a id="l00574" name="l00574"></a><span class="lineno">  574</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00575" name="l00575"></a><span class="lineno">  575</span><span class="comment">   * Equivalent to 2-argument schedule_from_now() except one specifies an absolute time point instead of wait duration.</span></div>
<div class="line"><a id="l00576" name="l00576"></a><span class="lineno">  576</span><span class="comment">   *</span></div>
<div class="line"><a id="l00577" name="l00577"></a><span class="lineno">  577</span><span class="comment">   * @warning See schedule_from_now() warning.</span></div>
<div class="line"><a id="l00578" name="l00578"></a><span class="lineno">  578</span><span class="comment">   *</span></div>
<div class="line"><a id="l00579" name="l00579"></a><span class="lineno">  579</span><span class="comment">   * @param at</span></div>
<div class="line"><a id="l00580" name="l00580"></a><span class="lineno">  580</span><span class="comment">   *        See util::schedule_task_at().</span></div>
<div class="line"><a id="l00581" name="l00581"></a><span class="lineno">  581</span><span class="comment">   * @param task</span></div>
<div class="line"><a id="l00582" name="l00582"></a><span class="lineno">  582</span><span class="comment">   *        See schedule_from_now().</span></div>
<div class="line"><a id="l00583" name="l00583"></a><span class="lineno">  583</span><span class="comment">   * @return See schedule_from_now().</span></div>
<div class="line"><a id="l00584" name="l00584"></a><span class="lineno">  584</span><span class="comment">   */</span></div>
<div class="line"><a id="l00585" name="l00585"></a><span class="lineno"><a class="line" href="classflow_1_1async_1_1Concurrent__task__loop.html#ad0ca0710d990c15cb9ea31535bea24cc">  585</a></span>  <span class="keyword">virtual</span> <a class="code hl_typedef" href="namespaceflow_1_1util.html#aa0d10f5a906b3229f48979aa43e9ff7e">util::Scheduled_task_handle</a> <a class="code hl_function" href="classflow_1_1async_1_1Concurrent__task__loop.html#ad0ca0710d990c15cb9ea31535bea24cc">schedule_at</a>(<span class="keyword">const</span> <a class="code hl_typedef" href="namespaceflow.html#a9d9cc2eeb10d398cff5591d446b763b8">Fine_time_pt</a>&amp; at, <a class="code hl_class" href="classflow_1_1Function.html">Scheduled_task</a>&amp;&amp; task) = 0;</div>
<div class="line"><a id="l00586" name="l00586"></a><span class="lineno">  586</span><span class="comment"></span> </div>
<div class="line"><a id="l00587" name="l00587"></a><span class="lineno">  587</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00588" name="l00588"></a><span class="lineno">  588</span><span class="comment">   * Equivalent to 3-argument post() but execution is scheduled for later, after the given time period passes.</span></div>
<div class="line"><a id="l00589" name="l00589"></a><span class="lineno">  589</span><span class="comment">   *</span></div>
<div class="line"><a id="l00590" name="l00590"></a><span class="lineno">  590</span><span class="comment">   * The semantics are, in all ways in which this differs from 3-argument post(), those of</span></div>
<div class="line"><a id="l00591" name="l00591"></a><span class="lineno">  591</span><span class="comment">   * util::schedule_task_from_now().  This includes the meaning of the returned value and the nature of</span></div>
<div class="line"><a id="l00592" name="l00592"></a><span class="lineno">  592</span><span class="comment">   * util::Scheduled_task.</span></div>
<div class="line"><a id="l00593" name="l00593"></a><span class="lineno">  593</span><span class="comment">   *</span></div>
<div class="line"><a id="l00594" name="l00594"></a><span class="lineno">  594</span><span class="comment">   * @warning See other schedule_from_now() warning.</span></div>
<div class="line"><a id="l00595" name="l00595"></a><span class="lineno">  595</span><span class="comment">   *</span></div>
<div class="line"><a id="l00596" name="l00596"></a><span class="lineno">  596</span><span class="comment">   * @param op</span></div>
<div class="line"><a id="l00597" name="l00597"></a><span class="lineno">  597</span><span class="comment">   *        See 3-argument post().</span></div>
<div class="line"><a id="l00598" name="l00598"></a><span class="lineno">  598</span><span class="comment">   * @param from_now</span></div>
<div class="line"><a id="l00599" name="l00599"></a><span class="lineno">  599</span><span class="comment">   *        See util::schedule_task_from_now().</span></div>
<div class="line"><a id="l00600" name="l00600"></a><span class="lineno">  600</span><span class="comment">   * @param task</span></div>
<div class="line"><a id="l00601" name="l00601"></a><span class="lineno">  601</span><span class="comment">   *        The task to execute within `*this`, subject to `op` constraints, unless successfully canceled.</span></div>
<div class="line"><a id="l00602" name="l00602"></a><span class="lineno">  602</span><span class="comment">   *        `task` object itself may be `move`d and saved.</span></div>
<div class="line"><a id="l00603" name="l00603"></a><span class="lineno">  603</span><span class="comment">   * @return See util::schedule_task_from_now().</span></div>
<div class="line"><a id="l00604" name="l00604"></a><span class="lineno">  604</span><span class="comment">   */</span></div>
<div class="line"><a id="l00605" name="l00605"></a><span class="lineno"><a class="line" href="classflow_1_1async_1_1Concurrent__task__loop.html#af3b04e2c7c2c8ee484a38b1156f8acc0">  605</a></span>  <span class="keyword">virtual</span> <a class="code hl_typedef" href="namespaceflow_1_1util.html#aa0d10f5a906b3229f48979aa43e9ff7e">util::Scheduled_task_handle</a> <a class="code hl_function" href="classflow_1_1async_1_1Concurrent__task__loop.html#af3b04e2c7c2c8ee484a38b1156f8acc0">schedule_from_now</a>(<span class="keyword">const</span> <a class="code hl_typedef" href="namespaceflow_1_1async.html#a024042c64b7dc544a7a5587afa4b1949">Op</a>&amp; op,</div>
<div class="line"><a id="l00606" name="l00606"></a><span class="lineno">  606</span>                                                        <span class="keyword">const</span> <a class="code hl_typedef" href="namespaceflow.html#a48799f1263cdeedec125be51a3db2b79">Fine_duration</a>&amp; from_now, <a class="code hl_class" href="classflow_1_1Function.html">Scheduled_task</a>&amp;&amp; task) = 0;</div>
<div class="line"><a id="l00607" name="l00607"></a><span class="lineno">  607</span><span class="comment"></span> </div>
<div class="line"><a id="l00608" name="l00608"></a><span class="lineno">  608</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00609" name="l00609"></a><span class="lineno">  609</span><span class="comment">   * Equivalent to 3-argument schedule_from_now() except one specifies an absolute time point instead of wait duration.</span></div>
<div class="line"><a id="l00610" name="l00610"></a><span class="lineno">  610</span><span class="comment">   *</span></div>
<div class="line"><a id="l00611" name="l00611"></a><span class="lineno">  611</span><span class="comment">   * @warning See schedule_from_now() warning.</span></div>
<div class="line"><a id="l00612" name="l00612"></a><span class="lineno">  612</span><span class="comment">   *</span></div>
<div class="line"><a id="l00613" name="l00613"></a><span class="lineno">  613</span><span class="comment">   * @param op</span></div>
<div class="line"><a id="l00614" name="l00614"></a><span class="lineno">  614</span><span class="comment">   *        See 3-argument post().</span></div>
<div class="line"><a id="l00615" name="l00615"></a><span class="lineno">  615</span><span class="comment">   * @param at</span></div>
<div class="line"><a id="l00616" name="l00616"></a><span class="lineno">  616</span><span class="comment">   *        See util::schedule_task_at().</span></div>
<div class="line"><a id="l00617" name="l00617"></a><span class="lineno">  617</span><span class="comment">   * @param task</span></div>
<div class="line"><a id="l00618" name="l00618"></a><span class="lineno">  618</span><span class="comment">   *        See schedule_from_now().</span></div>
<div class="line"><a id="l00619" name="l00619"></a><span class="lineno">  619</span><span class="comment">   * @return See schedule_from_now().</span></div>
<div class="line"><a id="l00620" name="l00620"></a><span class="lineno">  620</span><span class="comment">   */</span></div>
<div class="line"><a id="l00621" name="l00621"></a><span class="lineno"><a class="line" href="classflow_1_1async_1_1Concurrent__task__loop.html#ab1961159746ebe8b1787eadfbf728287">  621</a></span>  <span class="keyword">virtual</span> <a class="code hl_typedef" href="namespaceflow_1_1util.html#aa0d10f5a906b3229f48979aa43e9ff7e">util::Scheduled_task_handle</a> <a class="code hl_function" href="classflow_1_1async_1_1Concurrent__task__loop.html#ab1961159746ebe8b1787eadfbf728287">schedule_at</a>(<span class="keyword">const</span> <a class="code hl_typedef" href="namespaceflow_1_1async.html#a024042c64b7dc544a7a5587afa4b1949">Op</a>&amp; op,</div>
<div class="line"><a id="l00622" name="l00622"></a><span class="lineno">  622</span>                                                  <span class="keyword">const</span> <a class="code hl_typedef" href="namespaceflow.html#a9d9cc2eeb10d398cff5591d446b763b8">Fine_time_pt</a>&amp; at, <a class="code hl_class" href="classflow_1_1Function.html">Scheduled_task</a>&amp;&amp; task) = 0;</div>
<div class="line"><a id="l00623" name="l00623"></a><span class="lineno">  623</span><span class="comment"></span> </div>
<div class="line"><a id="l00624" name="l00624"></a><span class="lineno">  624</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00625" name="l00625"></a><span class="lineno">  625</span><span class="comment">   * Returns a pointer to *an* internal util::Task_engine (a/k/a boost.asio `io_context`) for the purpose of</span></div>
<div class="line"><a id="l00626" name="l00626"></a><span class="lineno">  626</span><span class="comment">   * performing a boost.asio `async_*()` action on some boost.asio I/O object in the immediate near future.</span></div>
<div class="line"><a id="l00627" name="l00627"></a><span class="lineno">  627</span><span class="comment">   *</span></div>
<div class="line"><a id="l00628" name="l00628"></a><span class="lineno">  628</span><span class="comment">   * The mechanics of using this are explained in Concurrent_task_loop doc header.  Using this in any other</span></div>
<div class="line"><a id="l00629" name="l00629"></a><span class="lineno">  629</span><span class="comment">   * fashion may lead to undefined behavior, while `*this` exists.</span></div>
<div class="line"><a id="l00630" name="l00630"></a><span class="lineno">  630</span><span class="comment">   *</span></div>
<div class="line"><a id="l00631" name="l00631"></a><span class="lineno">  631</span><span class="comment">   * @return A mutable util::Task_engine to use soon.  Informally, the sooner one calls the intended `async_*()` action</span></div>
<div class="line"><a id="l00632" name="l00632"></a><span class="lineno">  632</span><span class="comment">   *         on it, the more effective the internal load-balancing.  Formally, it is *allowed* to use it as long as</span></div>
<div class="line"><a id="l00633" name="l00633"></a><span class="lineno">  633</span><span class="comment">   *         `*this` exists (pre-destructor) and even beyond that, though any use beyond that point would pass the</span></div>
<div class="line"><a id="l00634" name="l00634"></a><span class="lineno">  634</span><span class="comment">   *         reponsibility on providing thread(s) to `run()` in becomes the user&#39;s.</span></div>
<div class="line"><a id="l00635" name="l00635"></a><span class="lineno">  635</span><span class="comment">   */</span></div>
<div class="line"><a id="l00636" name="l00636"></a><span class="lineno"><a class="line" href="classflow_1_1async_1_1Concurrent__task__loop.html#ac446f6bfed9fb54d073a5f3f578ec4bb">  636</a></span>  <span class="keyword">virtual</span> <a class="code hl_typedef" href="namespaceflow_1_1async.html#a968806f54b14c697fd76b3339a2bdbbf">Task_engine_ptr</a> <a class="code hl_function" href="classflow_1_1async_1_1Concurrent__task__loop.html#ac446f6bfed9fb54d073a5f3f578ec4bb">task_engine</a>() = 0;</div>
<div class="line"><a id="l00637" name="l00637"></a><span class="lineno">  637</span>}; <span class="comment">// class Concurrent_task_loop</span></div>
<div class="line"><a id="l00638" name="l00638"></a><span class="lineno">  638</span> </div>
<div class="line"><a id="l00639" name="l00639"></a><span class="lineno">  639</span><span class="comment">// Free functions: in *_fwd.hpp.</span></div>
<div class="line"><a id="l00640" name="l00640"></a><span class="lineno">  640</span> </div>
<div class="line"><a id="l00641" name="l00641"></a><span class="lineno">  641</span>} <span class="comment">// namespace flow::async</span></div>
<div class="line"><a id="l00642" name="l00642"></a><span class="lineno">  642</span> </div>
<div class="line"><a id="l00643" name="l00643"></a><span class="lineno">  643</span><span class="comment">// Macros.</span></div>
<div class="line"><a id="l00644" name="l00644"></a><span class="lineno">  644</span> </div>
<div class="line"><a id="l00645" name="l00645"></a><span class="lineno">  645</span><span class="preprocessor">#ifdef FLOW_DOXYGEN_ONLY </span><span class="comment">// Compiler ignores; Doxygen sees.</span></div>
<div class="line"><a id="l00646" name="l00646"></a><span class="lineno">  646</span><span class="comment"></span> </div>
<div class="line"><a id="l00647" name="l00647"></a><span class="lineno">  647</span><span class="comment">/**</span></div>
<div class="line"><a id="l00648" name="l00648"></a><span class="lineno">  648</span><span class="comment"> * Macro set to `1` (else `0`) if and only if natively the pthread API allows one to set thread-to-core</span></div>
<div class="line"><a id="l00649" name="l00649"></a><span class="lineno">  649</span><span class="comment"> * affinity.  This API, if available, is an extension of POSIX and not always available.</span></div>
<div class="line"><a id="l00650" name="l00650"></a><span class="lineno">  650</span><span class="comment"> *</span></div>
<div class="line"><a id="l00651" name="l00651"></a><span class="lineno">  651</span><span class="comment"> * The macro conceptually belongs to the flow::async namespace,</span></div>
<div class="line"><a id="l00652" name="l00652"></a><span class="lineno">  652</span><span class="comment"> * hence the prefix.</span></div>
<div class="line"><a id="l00653" name="l00653"></a><span class="lineno">  653</span><span class="comment"> *</span></div>
<div class="line"><a id="l00654" name="l00654"></a><span class="lineno">  654</span><span class="comment"> * @see #FLOW_ASYNC_HW_THREAD_AFFINITY_MACH_VIA_POLICY_TAG</span></div>
<div class="line"><a id="l00655" name="l00655"></a><span class="lineno">  655</span><span class="comment"> */</span></div>
<div class="line"><a id="l00656" name="l00656"></a><span class="lineno"><a class="line" href="concurrent__task__loop_8hpp.html#abdde86e8129cc056ef4c7dc2cafca8a7">  656</a></span><span class="preprocessor">#  define FLOW_ASYNC_HW_THREAD_AFFINITY_PTHREAD_VIA_CORE_IDX</span></div>
<div class="line"><a id="l00657" name="l00657"></a><span class="lineno">  657</span><span class="comment"></span> </div>
<div class="line"><a id="l00658" name="l00658"></a><span class="lineno">  658</span><span class="comment">/**</span></div>
<div class="line"><a id="l00659" name="l00659"></a><span class="lineno">  659</span><span class="comment"> * Macro set to `1` (else `0`) if and only if natively there is Mach kernel API that allows to set thread-to-core</span></div>
<div class="line"><a id="l00660" name="l00660"></a><span class="lineno">  660</span><span class="comment"> * affinity using the policy tag mechanism.  This is specific to Mac kernels (used in Darwin/Mac) and not all of</span></div>
<div class="line"><a id="l00661" name="l00661"></a><span class="lineno">  661</span><span class="comment"> * them.</span></div>
<div class="line"><a id="l00662" name="l00662"></a><span class="lineno">  662</span><span class="comment"> *</span></div>
<div class="line"><a id="l00663" name="l00663"></a><span class="lineno">  663</span><span class="comment"> * The macro conceptually belongs to the flow::async namespace,</span></div>
<div class="line"><a id="l00664" name="l00664"></a><span class="lineno">  664</span><span class="comment"> * hence the prefix.</span></div>
<div class="line"><a id="l00665" name="l00665"></a><span class="lineno">  665</span><span class="comment"> *</span></div>
<div class="line"><a id="l00666" name="l00666"></a><span class="lineno">  666</span><span class="comment"> * @see #FLOW_ASYNC_HW_THREAD_AFFINITY_PTHREAD_VIA_CORE_IDX</span></div>
<div class="line"><a id="l00667" name="l00667"></a><span class="lineno">  667</span><span class="comment"> */</span></div>
<div class="line"><a id="l00668" name="l00668"></a><span class="lineno"><a class="line" href="concurrent__task__loop_8hpp.html#acfbcdb498fb2ebbeae127cb5a777bb29">  668</a></span><span class="preprocessor">#  define FLOW_ASYNC_HW_THREAD_AFFINITY_MACH_VIA_POLICY_TAG</span></div>
<div class="line"><a id="l00669" name="l00669"></a><span class="lineno">  669</span> </div>
<div class="line"><a id="l00670" name="l00670"></a><span class="lineno">  670</span><span class="preprocessor">#else </span><span class="comment">// if !defined(FLOW_DOXYGEN_ONLY)</span></div>
<div class="line"><a id="l00671" name="l00671"></a><span class="lineno">  671</span> </div>
<div class="line"><a id="l00672" name="l00672"></a><span class="lineno">  672</span><span class="comment">// Now the actual definitions compiler sees (Doxygen ignores).</span></div>
<div class="line"><a id="l00673" name="l00673"></a><span class="lineno">  673</span> </div>
<div class="line"><a id="l00674" name="l00674"></a><span class="lineno">  674</span><span class="preprocessor">#  ifdef FLOW_OS_MAC</span></div>
<div class="line"><a id="l00675" name="l00675"></a><span class="lineno">  675</span><span class="preprocessor">#    define FLOW_ASYNC_HW_THREAD_AFFINITY_PTHREAD_VIA_CORE_IDX 0</span></div>
<div class="line"><a id="l00676" name="l00676"></a><span class="lineno">  676</span><span class="preprocessor">#    define FLOW_ASYNC_HW_THREAD_AFFINITY_MACH_VIA_POLICY_TAG 1</span></div>
<div class="line"><a id="l00677" name="l00677"></a><span class="lineno">  677</span><span class="preprocessor">#  elif defined(FLOW_OS_LINUX)</span></div>
<div class="line"><a id="l00678" name="l00678"></a><span class="lineno">  678</span><span class="preprocessor">#    define FLOW_ASYNC_HW_THREAD_AFFINITY_PTHREAD_VIA_CORE_IDX 1</span></div>
<div class="line"><a id="l00679" name="l00679"></a><span class="lineno">  679</span><span class="preprocessor">#    define FLOW_ASYNC_HW_THREAD_AFFINITY_MACH_VIA_POLICY_TAG 0</span></div>
<div class="line"><a id="l00680" name="l00680"></a><span class="lineno">  680</span><span class="preprocessor">#  else</span></div>
<div class="line"><a id="l00681" name="l00681"></a><span class="lineno">  681</span><span class="keyword">static_assert</span>(<span class="keyword">false</span>, <span class="stringliteral">&quot;We only know how to deal with thread-core affinities in Darwin/Mac and Linux.&quot;</span>);</div>
<div class="line"><a id="l00682" name="l00682"></a><span class="lineno">  682</span><span class="preprocessor">#  endif</span></div>
<div class="line"><a id="l00683" name="l00683"></a><span class="lineno">  683</span> </div>
<div class="line"><a id="l00684" name="l00684"></a><span class="lineno">  684</span><span class="preprocessor">#endif </span><span class="comment">// elif !defined(FLOW_DOXYGEN_ONLY)</span></div>
<div class="line"><a id="l00685" name="l00685"></a><span class="lineno">  685</span> </div>
<div class="line"><a id="l00686" name="l00686"></a><span class="lineno">  686</span><span class="keyword">namespace </span><a class="code hl_namespace" href="namespaceflow_1_1async.html">flow::async</a></div>
<div class="line"><a id="l00687" name="l00687"></a><span class="lineno">  687</span>{</div>
<div class="line"><a id="l00688" name="l00688"></a><span class="lineno">  688</span><span class="comment">// Template implementations.</span></div>
<div class="line"><a id="l00689" name="l00689"></a><span class="lineno">  689</span> </div>
<div class="line"><a id="l00690" name="l00690"></a><span class="lineno">  690</span><span class="keyword">template</span>&lt;<span class="keyword">typename</span> Handler&gt;</div>
<div class="line"><a id="l00691" name="l00691"></a><span class="lineno"><a class="line" href="namespaceflow_1_1async.html#af90c1e763d49c3f3033a74871e897394">  691</a></span><span class="keyword">auto</span> <a class="code hl_function" href="namespaceflow_1_1async.html#af90c1e763d49c3f3033a74871e897394">asio_handler_via_op</a>(<a class="code hl_class" href="classflow_1_1async_1_1Concurrent__task__loop.html">Concurrent_task_loop</a>* loop, <span class="keyword">const</span> <a class="code hl_typedef" href="namespaceflow_1_1async.html#a024042c64b7dc544a7a5587afa4b1949">Op</a>&amp; op, Handler&amp;&amp; handler)</div>
<div class="line"><a id="l00692" name="l00692"></a><span class="lineno">  692</span>{</div>
<div class="line"><a id="l00693" name="l00693"></a><span class="lineno">  693</span>  <span class="comment">/* To understand this -- though it is rather basic boiler-plate if one is familiar with lambdas and boost.asio --</span></div>
<div class="line"><a id="l00694" name="l00694"></a><span class="lineno">  694</span><span class="comment">   * in context, read the relevant section of Concurrent_task_loop doc header.  */</span></div>
<div class="line"><a id="l00695" name="l00695"></a><span class="lineno">  695</span>  <span class="keywordflow">return</span> [loop, op, handler = std::move(handler)](<span class="keyword">auto</span>... params) <span class="keyword">mutable</span></div>
<div class="line"><a id="l00696" name="l00696"></a><span class="lineno">  696</span>  {</div>
<div class="line"><a id="l00697" name="l00697"></a><span class="lineno">  697</span>    loop-&gt;<a class="code hl_function" href="classflow_1_1async_1_1Concurrent__task__loop.html#a24f96f97ee24bfabb06c8609bc0e94a6">post</a>(op,</div>
<div class="line"><a id="l00698" name="l00698"></a><span class="lineno">  698</span>               [handler = std::move(handler), <span class="comment">// Avoid copying handler again.  Move it instead.</span></div>
<div class="line"><a id="l00699" name="l00699"></a><span class="lineno">  699</span>                params...]()</div>
<div class="line"><a id="l00700" name="l00700"></a><span class="lineno">  700</span>    {</div>
<div class="line"><a id="l00701" name="l00701"></a><span class="lineno">  701</span>      handler(params...);</div>
<div class="line"><a id="l00702" name="l00702"></a><span class="lineno">  702</span>    }, <a class="code hl_enumvalue" href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485aff6bc53ee6c14f2eee463c06d9dff01f">Synchronicity::S_OPPORTUNISTIC_SYNC_ELSE_ASYNC</a>);</div>
<div class="line"><a id="l00703" name="l00703"></a><span class="lineno">  703</span>    <span class="comment">/* Attn: That last argument means if we&#39;re already in the proper thread, then run `handler(args...);`</span></div>
<div class="line"><a id="l00704" name="l00704"></a><span class="lineno">  704</span><span class="comment">     * synchronously right now.  This is a perf win -- particularly when *loop is really a Segregated_thread_task_loop,</span></div>
<div class="line"><a id="l00705" name="l00705"></a><span class="lineno">  705</span><span class="comment">     * when this win will be in effect every single time -- but is it safe?  Yes: The entirety of the intended task</span></div>
<div class="line"><a id="l00706" name="l00706"></a><span class="lineno">  706</span><span class="comment">     * *is* `handler(args...)`, and the present { body } has already been post()ed in its entirety and is</span></div>
<div class="line"><a id="l00707" name="l00707"></a><span class="lineno">  707</span><span class="comment">     * executing, hence we&#39;re adding nothing unsafe by executing the handler synchronously now. */</span></div>
<div class="line"><a id="l00708" name="l00708"></a><span class="lineno">  708</span>  };</div>
<div class="line"><a id="l00709" name="l00709"></a><span class="lineno">  709</span> </div>
<div class="line"><a id="l00710" name="l00710"></a><span class="lineno">  710</span>  <span class="comment">/* Subtleties regarding `params...` and `auto`:</span></div>
<div class="line"><a id="l00711" name="l00711"></a><span class="lineno">  711</span><span class="comment">   * Firstly, if not familiar with this crazy particular use of `auto` (on `params`), it&#39;s something like this</span></div>
<div class="line"><a id="l00712" name="l00712"></a><span class="lineno">  712</span><span class="comment">   * (cppreference.com, in its big page on lambdas, explains this is called a &quot;generic lambda&quot;):</span></div>
<div class="line"><a id="l00713" name="l00713"></a><span class="lineno">  713</span><span class="comment">   * The params... pack expands to the arg types based on what Handler really is, in that instantiation of the</span></div>
<div class="line"><a id="l00714" name="l00714"></a><span class="lineno">  714</span><span class="comment">   * asio_handler_via_op() template; meaning if Handler is, say, Function&lt;void (int a, int b)&gt;, then</span></div>
<div class="line"><a id="l00715" name="l00715"></a><span class="lineno">  715</span><span class="comment">   * params... = int, int -- because of the invocation of `handler()` inside the *body* of the returned lambda.</span></div>
<div class="line"><a id="l00716" name="l00716"></a><span class="lineno">  716</span><span class="comment">   * Hence the returned object is a function object that takes the same types of arguments, magically.</span></div>
<div class="line"><a id="l00717" name="l00717"></a><span class="lineno">  717</span><span class="comment">   * Secondly, and this is where it gets subtle, notice what we do with params... within the returned lambda:</span></div>
<div class="line"><a id="l00718" name="l00718"></a><span class="lineno">  718</span><span class="comment">   * we *capture* params..., so that we can post() a no-arg handler onto *loop; and within the body of that no-arg</span></div>
<div class="line"><a id="l00719" name="l00719"></a><span class="lineno">  719</span><span class="comment">   * handler we will finally (when boost.asio actually executes the post()ed thing at some point) invoke the handler,</span></div>
<div class="line"><a id="l00720" name="l00720"></a><span class="lineno">  720</span><span class="comment">   * passing it `params...`.  The subtlety is that each actual arg in the params... pack is *copied* when thus</span></div>
<div class="line"><a id="l00721" name="l00721"></a><span class="lineno">  721</span><span class="comment">   * captured.  Ideally, for performance, we&#39;d write something like `params = std::move(params)...`, but this is not</span></div>
<div class="line"><a id="l00722" name="l00722"></a><span class="lineno">  722</span><span class="comment">   * supported (at least in C++17); only capturing a pack by copy is supported -- using a pack in an init-capture</span></div>
<div class="line"><a id="l00723" name="l00723"></a><span class="lineno">  723</span><span class="comment">   * ([blah = blah]) isn&#39;t supported.  To that end a standards edit was proposed:</span></div>
<div class="line"><a id="l00724" name="l00724"></a><span class="lineno">  724</span><span class="comment">   *   http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0780r0.html</span></div>
<div class="line"><a id="l00725" name="l00725"></a><span class="lineno">  725</span><span class="comment">   * Apparently C++20 accepted this in slightly modified (syntactically) form, and indeed on coliru.com one can write</span></div>
<div class="line"><a id="l00726" name="l00726"></a><span class="lineno">  726</span><span class="comment">   * `...params = std::move(params)` and build it with --std=c++20.  In the meantime (C++14, C++17) one *could* get the</span></div>
<div class="line"><a id="l00727" name="l00727"></a><span class="lineno">  727</span><span class="comment">   * desired behavior by using a strained tuple&lt;&gt; construction (see the above link which suggests it as a work-around).</span></div>
<div class="line"><a id="l00728" name="l00728"></a><span class="lineno">  728</span><span class="comment">   * However, I (ygoldfel) did not do it; I am just copying it.  Reason: Well, it&#39;s much easier to read.</span></div>
<div class="line"><a id="l00729" name="l00729"></a><span class="lineno">  729</span><span class="comment">   * Perf-wise, however, the reason is: boost.asio out-of-the-box handler types all take little scalars (size_t,</span></div>
<div class="line"><a id="l00730" name="l00730"></a><span class="lineno">  730</span><span class="comment">   * Error_code) which are fine to copy (std::move() would just copy them anyway).  That said, boost.asio can be used</span></div>
<div class="line"><a id="l00731" name="l00731"></a><span class="lineno">  731</span><span class="comment">   * with custom types; and indeed for example flow::net_flow::asio::Server_socket::async_accept() works with handlers</span></div>
<div class="line"><a id="l00732" name="l00732"></a><span class="lineno">  732</span><span class="comment">   * that take a shared_ptr&lt;&gt; arg: copying that would increment a ref-count/later decrement it... whereas a move()</span></div>
<div class="line"><a id="l00733" name="l00733"></a><span class="lineno">  733</span><span class="comment">   * would do neither.  So it&#39;s not quite free in all cases -- close enough though in my opinion.</span></div>
<div class="line"><a id="l00734" name="l00734"></a><span class="lineno">  734</span><span class="comment">   *</span></div>
<div class="line"><a id="l00735" name="l00735"></a><span class="lineno">  735</span><span class="comment">   * @todo As of this writing we&#39;ve recently moved to C++17 (months after this code was written originally);</span></div>
<div class="line"><a id="l00736" name="l00736"></a><span class="lineno">  736</span><span class="comment">   * which gains std::apply().  The tuple&lt;&gt;+apply() trick isn&#39;t *so* hard to read/write.  Maybe do so.</span></div>
<div class="line"><a id="l00737" name="l00737"></a><span class="lineno">  737</span><span class="comment">   * @todo With C++20 -- if that ever happens -- can just write it so nicely: [...params = std::move(params)];</span></div>
<div class="line"><a id="l00738" name="l00738"></a><span class="lineno">  738</span><span class="comment">   * best of all worlds. */</span></div>
<div class="line"><a id="l00739" name="l00739"></a><span class="lineno">  739</span> </div>
<div class="line"><a id="l00740" name="l00740"></a><span class="lineno">  740</span>  <span class="comment">// ---</span></div>
<div class="line"><a id="l00741" name="l00741"></a><span class="lineno">  741</span> </div>
<div class="line"><a id="l00742" name="l00742"></a><span class="lineno">  742</span>  <span class="comment">/* Lastly let&#39;s deal with the possibility that *loop is a Timed_concurrent_task_loop decorator of an actual</span></div>
<div class="line"><a id="l00743" name="l00743"></a><span class="lineno">  743</span><span class="comment">   * Concurrent_task_loop.  The good news is we&#39;ve already ensured `handler()` itself gets timed: we L-&gt;post()ed,</span></div>
<div class="line"><a id="l00744" name="l00744"></a><span class="lineno">  744</span><span class="comment">   * and L-&gt;post() does the right thing by definition when L is indeed Timed_....  However the loop-&gt;post() thingie</span></div>
<div class="line"><a id="l00745" name="l00745"></a><span class="lineno">  745</span><span class="comment">   * we executed to make that happen -- that won&#39;t be timed, if we simply return posting_handler; after all</span></div>
<div class="line"><a id="l00746" name="l00746"></a><span class="lineno">  746</span><span class="comment">   * they&#39;ll just do async_&lt;something&gt;(..., posting_handler), and that&#39;ll be that.  One *could* try to</span></div>
<div class="line"><a id="l00747" name="l00747"></a><span class="lineno">  747</span><span class="comment">   * conditionally (via dynamic_cast&lt;&gt; RTTI check) wrap the above in asio_handler_timed() if *loop is</span></div>
<div class="line"><a id="l00748" name="l00748"></a><span class="lineno">  748</span><span class="comment">   * really a Timed_concurrent_task_loop; otherwise just return the above.  However then `auto` can fail to compile,</span></div>
<div class="line"><a id="l00749" name="l00749"></a><span class="lineno">  749</span><span class="comment">   * as the returned lambda function object type could be A in one case but B in another, for the same `Handler`;</span></div>
<div class="line"><a id="l00750" name="l00750"></a><span class="lineno">  750</span><span class="comment">   * and we&#39;re screwed.  So for now it&#39;s a @todo:</span></div>
<div class="line"><a id="l00751" name="l00751"></a><span class="lineno">  751</span><span class="comment">   *</span></div>
<div class="line"><a id="l00752" name="l00752"></a><span class="lineno">  752</span><span class="comment">   * @todo Enable the timing of the post()ing code above, not just handler() itself.  How?  Suppose the RTTI</span></div>
<div class="line"><a id="l00753" name="l00753"></a><span class="lineno">  753</span><span class="comment">   * check idea were workable (thought experiment).  Then:</span></div>
<div class="line"><a id="l00754" name="l00754"></a><span class="lineno">  754</span><span class="comment">   * This kind of use of RTTI to conditionally do or not do something immediately sets off alarms; the point</span></div>
<div class="line"><a id="l00755" name="l00755"></a><span class="lineno">  755</span><span class="comment">   * of interfaces is to do everything conditional through virtual.  But the whole point of</span></div>
<div class="line"><a id="l00756" name="l00756"></a><span class="lineno">  756</span><span class="comment">   * Timed_concurrent_task_loop&#39;s design is to *not* modify the core Concurrent_task_loop API but only decorate</span></div>
<div class="line"><a id="l00757" name="l00757"></a><span class="lineno">  757</span><span class="comment">   * its behavior.  To really solve this, I (ygoldfel) believe that a good-anyway rewrite of the</span></div>
<div class="line"><a id="l00758" name="l00758"></a><span class="lineno">  758</span><span class="comment">   * Concurrent_task_loop hierarchy is in order.  It really should have been a set of concept-implementing</span></div>
<div class="line"><a id="l00759" name="l00759"></a><span class="lineno">  759</span><span class="comment">   * classes (where Concurrent_task_loop would cease to exist as a class and be merely a duck-typing concept).</span></div>
<div class="line"><a id="l00760" name="l00760"></a><span class="lineno">  760</span><span class="comment">   * This would be a breaking change, but it would resolve a few issues.  1, asio_handler_via_op() could be coded</span></div>
<div class="line"><a id="l00761" name="l00761"></a><span class="lineno">  761</span><span class="comment">   * separately for each type of _loop, which would make it possible to not even add this intermediate post()</span></div>
<div class="line"><a id="l00762" name="l00762"></a><span class="lineno">  762</span><span class="comment">   * but instead simply do the right thing for each actual type of _loop: Cross_thread_task_loop would</span></div>
<div class="line"><a id="l00763" name="l00763"></a><span class="lineno">  763</span><span class="comment">   * fish out the Strand from the Op and bind that executor to `handler`; Segregated_thread_task_loop would</span></div>
<div class="line"><a id="l00764" name="l00764"></a><span class="lineno">  764</span><span class="comment">   * be a no-op (as the user must select the Op-appropriate Task_engine in the first place).  The perf</span></div>
<div class="line"><a id="l00765" name="l00765"></a><span class="lineno">  765</span><span class="comment">   * implications of such an approach would be pleasant.  And 2,</span></div>
<div class="line"><a id="l00766" name="l00766"></a><span class="lineno">  766</span><span class="comment">   * Timed_concurrent_task_loop&#39;s overload of asio_handler_via_op() would simply forward to the contained</span></div>
<div class="line"><a id="l00767" name="l00767"></a><span class="lineno">  767</span><span class="comment">   * Concurrent_task_loop&#39;s asio_handler_via_op() -- and then wrap the result in asio_handler_timed() and return</span></div>
<div class="line"><a id="l00768" name="l00768"></a><span class="lineno">  768</span><span class="comment">   * that.  Nice and clean.  Obviously then the way one uses the whole hierarchy would change and be a breaking</span></div>
<div class="line"><a id="l00769" name="l00769"></a><span class="lineno">  769</span><span class="comment">   * change -- but even that wouldn&#39;t be such a big deal; a virtual hierarchy could be built on top of these</span></div>
<div class="line"><a id="l00770" name="l00770"></a><span class="lineno">  770</span><span class="comment">   * concept-satisfying classes, if needed (and I doubt it&#39;s needed all that frequently in practice). */</span></div>
<div class="line"><a id="l00771" name="l00771"></a><span class="lineno">  771</span>} <span class="comment">// asio_handler_via_op()</span></div>
<div class="line"><a id="l00772" name="l00772"></a><span class="lineno">  772</span> </div>
<div class="line"><a id="l00773" name="l00773"></a><span class="lineno">  773</span>} <span class="comment">// namespace flow::async</span></div>
<div class="ttc" id="aasync__fwd_8hpp_html"><div class="ttname"><a href="async__fwd_8hpp.html">async_fwd.hpp</a></div></div>
<div class="ttc" id="aclassflow_1_1Function_html"><div class="ttname"><a href="classflow_1_1Function.html">flow::Function</a></div><div class="ttdef"><b>Definition:</b> <a href="common_8hpp_source.html#l00512">common.hpp:512</a></div></div>
<div class="ttc" id="aclassflow_1_1async_1_1Concurrent__task__loop_html"><div class="ttname"><a href="classflow_1_1async_1_1Concurrent__task__loop.html">flow::async::Concurrent_task_loop</a></div><div class="ttdoc">The core flow::async interface, providing an optionally multi-threaded thread pool onto which runnabl...</div><div class="ttdef"><b>Definition:</b> <a href="concurrent__task__loop_8hpp_source.html#l00322">concurrent_task_loop.hpp:324</a></div></div>
<div class="ttc" id="aclassflow_1_1async_1_1Concurrent__task__loop_html_a131335863b19446dbc349de181d4b5a1"><div class="ttname"><a href="classflow_1_1async_1_1Concurrent__task__loop.html#a131335863b19446dbc349de181d4b5a1">flow::async::Concurrent_task_loop::n_threads</a></div><div class="ttdeci">virtual size_t n_threads() const =0</div><div class="ttdoc">How many threads does start() start?</div></div>
<div class="ttc" id="aclassflow_1_1async_1_1Concurrent__task__loop_html_a24f96f97ee24bfabb06c8609bc0e94a6"><div class="ttname"><a href="classflow_1_1async_1_1Concurrent__task__loop.html#a24f96f97ee24bfabb06c8609bc0e94a6">flow::async::Concurrent_task_loop::post</a></div><div class="ttdeci">virtual void post(Task &amp;&amp;task, Synchronicity synchronicity=Synchronicity::S_ASYNC)=0</div><div class="ttdoc">Cause the given Task (function) to execute within the thread pool as soon as possible,...</div></div>
<div class="ttc" id="aclassflow_1_1async_1_1Concurrent__task__loop_html_a4ee1c5f5785af0bcc6aed0757981ffe3"><div class="ttname"><a href="classflow_1_1async_1_1Concurrent__task__loop.html#a4ee1c5f5785af0bcc6aed0757981ffe3">flow::async::Concurrent_task_loop::create_op</a></div><div class="ttdeci">virtual Op create_op()=0</div><div class="ttdoc">Return a new Op which can bundle together an arbitrary set of post()s that would result in the provid...</div></div>
<div class="ttc" id="aclassflow_1_1async_1_1Concurrent__task__loop_html_a54bd938b133103328a90d50823755358"><div class="ttname"><a href="classflow_1_1async_1_1Concurrent__task__loop.html#a54bd938b133103328a90d50823755358">flow::async::Concurrent_task_loop::per_thread_ops</a></div><div class="ttdeci">virtual const Op_list &amp; per_thread_ops()=0</div><div class="ttdoc">Returns the optional-use, pre-created collection of per-thread async::Op objects, such that the i-th ...</div></div>
<div class="ttc" id="aclassflow_1_1async_1_1Concurrent__task__loop_html_a7b9123d43e1cfae899b0e1bb52bb6dde"><div class="ttname"><a href="classflow_1_1async_1_1Concurrent__task__loop.html#a7b9123d43e1cfae899b0e1bb52bb6dde">flow::async::Concurrent_task_loop::~Concurrent_task_loop</a></div><div class="ttdeci">~Concurrent_task_loop() override</div><div class="ttdoc">Any implementing subclass's destructor shall execute stop() – see its doc header please – and then cl...</div></div>
<div class="ttc" id="aclassflow_1_1async_1_1Concurrent__task__loop_html_aa164fb1fe1b3d7fce0de0174d77ea396"><div class="ttname"><a href="classflow_1_1async_1_1Concurrent__task__loop.html#aa164fb1fe1b3d7fce0de0174d77ea396">flow::async::Concurrent_task_loop::Thread_init_func</a></div><div class="ttdeci">Function&lt; void(size_t thread_idx)&gt; Thread_init_func</div><div class="ttdoc">Short-hand for the thread-initializer-function optional arg type to start().</div><div class="ttdef"><b>Definition:</b> <a href="concurrent__task__loop_8hpp_source.html#l00329">concurrent_task_loop.hpp:329</a></div></div>
<div class="ttc" id="aclassflow_1_1async_1_1Concurrent__task__loop_html_aadadb5b8b6c40ddc86c205de1b8f25b1"><div class="ttname"><a href="classflow_1_1async_1_1Concurrent__task__loop.html#aadadb5b8b6c40ddc86c205de1b8f25b1">flow::async::Concurrent_task_loop::stop</a></div><div class="ttdeci">virtual void stop()=0</div><div class="ttdoc">Waits for any ongoing task(s)/completion handler(s) to return; then prevents any further-queued such ...</div></div>
<div class="ttc" id="aclassflow_1_1async_1_1Concurrent__task__loop_html_ab0e31275441218c4d77df0730fd5e8f7"><div class="ttname"><a href="classflow_1_1async_1_1Concurrent__task__loop.html#ab0e31275441218c4d77df0730fd5e8f7">flow::async::Concurrent_task_loop::post</a></div><div class="ttdeci">virtual void post(const Op &amp;op, Task &amp;&amp;task, Synchronicity synchronicity=Synchronicity::S_ASYNC)=0</div><div class="ttdoc">Identical to the other post() with the added constraint that no other Task also similarly posted with...</div></div>
<div class="ttc" id="aclassflow_1_1async_1_1Concurrent__task__loop_html_ab1961159746ebe8b1787eadfbf728287"><div class="ttname"><a href="classflow_1_1async_1_1Concurrent__task__loop.html#ab1961159746ebe8b1787eadfbf728287">flow::async::Concurrent_task_loop::schedule_at</a></div><div class="ttdeci">virtual util::Scheduled_task_handle schedule_at(const Op &amp;op, const Fine_time_pt &amp;at, Scheduled_task &amp;&amp;task)=0</div><div class="ttdoc">Equivalent to 3-argument schedule_from_now() except one specifies an absolute time point instead of w...</div></div>
<div class="ttc" id="aclassflow_1_1async_1_1Concurrent__task__loop_html_ac446f6bfed9fb54d073a5f3f578ec4bb"><div class="ttname"><a href="classflow_1_1async_1_1Concurrent__task__loop.html#ac446f6bfed9fb54d073a5f3f578ec4bb">flow::async::Concurrent_task_loop::task_engine</a></div><div class="ttdeci">virtual Task_engine_ptr task_engine()=0</div><div class="ttdoc">Returns a pointer to an internal util::Task_engine (a/k/a boost.asio io_context) for the purpose of p...</div></div>
<div class="ttc" id="aclassflow_1_1async_1_1Concurrent__task__loop_html_ac6b98b440d52c079c22d7972c9b12e1b"><div class="ttname"><a href="classflow_1_1async_1_1Concurrent__task__loop.html#ac6b98b440d52c079c22d7972c9b12e1b">flow::async::Concurrent_task_loop::schedule_from_now</a></div><div class="ttdeci">virtual util::Scheduled_task_handle schedule_from_now(const Fine_duration &amp;from_now, Scheduled_task &amp;&amp;task)=0</div><div class="ttdoc">Equivalent to 2-argument post() but execution is scheduled for later, after the given time period pas...</div></div>
<div class="ttc" id="aclassflow_1_1async_1_1Concurrent__task__loop_html_ad0ca0710d990c15cb9ea31535bea24cc"><div class="ttname"><a href="classflow_1_1async_1_1Concurrent__task__loop.html#ad0ca0710d990c15cb9ea31535bea24cc">flow::async::Concurrent_task_loop::schedule_at</a></div><div class="ttdeci">virtual util::Scheduled_task_handle schedule_at(const Fine_time_pt &amp;at, Scheduled_task &amp;&amp;task)=0</div><div class="ttdoc">Equivalent to 2-argument schedule_from_now() except one specifies an absolute time point instead of w...</div></div>
<div class="ttc" id="aclassflow_1_1async_1_1Concurrent__task__loop_html_af3b04e2c7c2c8ee484a38b1156f8acc0"><div class="ttname"><a href="classflow_1_1async_1_1Concurrent__task__loop.html#af3b04e2c7c2c8ee484a38b1156f8acc0">flow::async::Concurrent_task_loop::schedule_from_now</a></div><div class="ttdeci">virtual util::Scheduled_task_handle schedule_from_now(const Op &amp;op, const Fine_duration &amp;from_now, Scheduled_task &amp;&amp;task)=0</div><div class="ttdoc">Equivalent to 3-argument post() but execution is scheduled for later, after the given time period pas...</div></div>
<div class="ttc" id="aclassflow_1_1async_1_1Concurrent__task__loop_html_afff5e62840791b309e178c5ddc26e594"><div class="ttname"><a href="classflow_1_1async_1_1Concurrent__task__loop.html#afff5e62840791b309e178c5ddc26e594">flow::async::Concurrent_task_loop::start</a></div><div class="ttdeci">virtual void start(Task &amp;&amp;init_task_or_empty=Task(), const Thread_init_func &amp;thread_init_func_or_empty=Thread_init_func())=0</div><div class="ttdoc">Starts all threads in the thread pool; any queued post()ed (and similar) tasks may begin executing im...</div></div>
<div class="ttc" id="aclassflow_1_1async_1_1Op__list_html"><div class="ttname"><a href="classflow_1_1async_1_1Op__list.html">flow::async::Op_list</a></div><div class="ttdoc">Simple, immutable vector-like sequence of N opaque async::Op objects, usually corresponding to N work...</div><div class="ttdef"><b>Definition:</b> <a href="op_8hpp_source.html#l00056">op.hpp:58</a></div></div>
<div class="ttc" id="aclassflow_1_1util_1_1Null__interface_html"><div class="ttname"><a href="classflow_1_1util_1_1Null__interface.html">flow::util::Null_interface</a></div><div class="ttdoc">An empty interface, consisting of nothing but a default virtual destructor, intended as a boiler-plat...</div><div class="ttdef"><b>Definition:</b> <a href="util_2util_8hpp_source.html#l00044">util.hpp:45</a></div></div>
<div class="ttc" id="anamespaceflow_1_1async_html"><div class="ttname"><a href="namespaceflow_1_1async.html">flow::async</a></div><div class="ttdoc">Flow module containing tools enabling multi-threaded event loops operating under the asynchronous-tas...</div><div class="ttdef"><b>Definition:</b> <a href="async__fwd_8hpp_source.html#l00074">async_fwd.hpp:75</a></div></div>
<div class="ttc" id="anamespaceflow_1_1async_html_a024042c64b7dc544a7a5587afa4b1949"><div class="ttname"><a href="namespaceflow_1_1async.html#a024042c64b7dc544a7a5587afa4b1949">flow::async::Op</a></div><div class="ttdeci">boost::any Op</div><div class="ttdoc">An object of this opaque type represents a collection of 1 or more async::Task, past or future,...</div><div class="ttdef"><b>Definition:</b> <a href="async__fwd_8hpp_source.html#l00153">async_fwd.hpp:153</a></div></div>
<div class="ttc" id="anamespaceflow_1_1async_html_a0a06794b16b72f2829ce3353557c8485"><div class="ttname"><a href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485">flow::async::Synchronicity</a></div><div class="ttdeci">Synchronicity</div><div class="ttdoc">Enumeration indicating the manner in which asio_exec_ctx_post(), and various boost....</div><div class="ttdef"><b>Definition:</b> <a href="async__fwd_8hpp_source.html#l00222">async_fwd.hpp:223</a></div></div>
<div class="ttc" id="anamespaceflow_1_1async_html_a0a06794b16b72f2829ce3353557c8485a4d7a5700444c0570af37b1f9bcc6eb1f"><div class="ttname"><a href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485a4d7a5700444c0570af37b1f9bcc6eb1f">flow::async::Synchronicity::S_ASYNC</a></div><div class="ttdeci">@ S_ASYNC</div><div class="ttdoc">Simply post the given task to execute asynchronously in some execution context – as soon as the conte...</div></div>
<div class="ttc" id="anamespaceflow_1_1async_html_a0a06794b16b72f2829ce3353557c8485aff6bc53ee6c14f2eee463c06d9dff01f"><div class="ttname"><a href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485aff6bc53ee6c14f2eee463c06d9dff01f">flow::async::Synchronicity::S_OPPORTUNISTIC_SYNC_ELSE_ASYNC</a></div><div class="ttdeci">@ S_OPPORTUNISTIC_SYNC_ELSE_ASYNC</div><div class="ttdoc">Execute the given task synchronously, if the scheduler determines that the calling thread is in its t...</div></div>
<div class="ttc" id="anamespaceflow_1_1async_html_a968806f54b14c697fd76b3339a2bdbbf"><div class="ttname"><a href="namespaceflow_1_1async.html#a968806f54b14c697fd76b3339a2bdbbf">flow::async::Task_engine_ptr</a></div><div class="ttdeci">boost::shared_ptr&lt; util::Task_engine &gt; Task_engine_ptr</div><div class="ttdoc">Short-hand for reference-counting pointer to a mutable util::Task_engine (a/k/a boost::asio::io_conte...</div><div class="ttdef"><b>Definition:</b> <a href="async__fwd_8hpp_source.html#l00198">async_fwd.hpp:198</a></div></div>
<div class="ttc" id="anamespaceflow_1_1async_html_af35fb65bdea1a3a92929ec2c4a6a6b72"><div class="ttname"><a href="namespaceflow_1_1async.html#af35fb65bdea1a3a92929ec2c4a6a6b72">flow::async::Task</a></div><div class="ttdeci">Function&lt; void()&gt; Task</div><div class="ttdoc">Short-hand for a task that can be posted for execution by a Concurrent_task_loop or flow::util::Task_...</div><div class="ttdef"><b>Definition:</b> <a href="async__fwd_8hpp_source.html#l00096">async_fwd.hpp:96</a></div></div>
<div class="ttc" id="anamespaceflow_1_1async_html_af90c1e763d49c3f3033a74871e897394"><div class="ttname"><a href="namespaceflow_1_1async.html#af90c1e763d49c3f3033a74871e897394">flow::async::asio_handler_via_op</a></div><div class="ttdeci">auto asio_handler_via_op(Concurrent_task_loop *loop, const Op &amp;op, Handler &amp;&amp;handler)</div><div class="ttdoc">Given a boost.asio completion handler handler for a boost.asio async_*() action on some boost....</div><div class="ttdef"><b>Definition:</b> <a href="concurrent__task__loop_8hpp_source.html#l00691">concurrent_task_loop.hpp:691</a></div></div>
<div class="ttc" id="anamespaceflow_1_1util_html_aa0d10f5a906b3229f48979aa43e9ff7e"><div class="ttname"><a href="namespaceflow_1_1util.html#aa0d10f5a906b3229f48979aa43e9ff7e">flow::util::Scheduled_task_handle</a></div><div class="ttdeci">boost::shared_ptr&lt; Scheduled_task_handle_state &gt; Scheduled_task_handle</div><div class="ttdoc">Black-box type that represents a handle to a scheduled task as scheduled by schedule_task_at() or sch...</div><div class="ttdef"><b>Definition:</b> <a href="sched__task__fwd_8hpp_source.html#l00045">sched_task_fwd.hpp:45</a></div></div>
<div class="ttc" id="anamespaceflow_html_a48799f1263cdeedec125be51a3db2b79"><div class="ttname"><a href="namespaceflow.html#a48799f1263cdeedec125be51a3db2b79">flow::Fine_duration</a></div><div class="ttdeci">Fine_clock::duration Fine_duration</div><div class="ttdoc">A high-res time duration as computed from two Fine_time_pts.</div><div class="ttdef"><b>Definition:</b> <a href="common_8hpp_source.html#l00416">common.hpp:416</a></div></div>
<div class="ttc" id="anamespaceflow_html_a9d9cc2eeb10d398cff5591d446b763b8"><div class="ttname"><a href="namespaceflow.html#a9d9cc2eeb10d398cff5591d446b763b8">flow::Fine_time_pt</a></div><div class="ttdeci">Fine_clock::time_point Fine_time_pt</div><div class="ttdoc">A high-res time point as returned by Fine_clock::now() and suitable for precise time math in general.</div><div class="ttdef"><b>Definition:</b> <a href="common_8hpp_source.html#l00413">common.hpp:413</a></div></div>
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